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INSULATION, THERMAL and ACOUSTICAL, Basics -- INT-201
This L-O-N-G article was contributed by Fletcher R Millmore, Titusville, PA, USA

Regarding Thermal and Acoustic Insulation for Cars

This discussion is not meant to be scientifically rigorous; the problem of energy transfer is the entire basis for the development of quantum physics. Rather, it is meant to provide the basic science on the subject as a practical guide to DIY improvements in the restoration of our wonderful cars. Readers in other parts of the world may need to substitute materials, but a good understanding of the science involved should serve you well. I have spent a lot of time looking at this problem and observing “real world” things like aging of materials, practicality of installation, etc. Any thoughts or additional useful information any reader comes up with are greatly appreciated.

Fundamentals

There are three mechanisms responsible for the transfer of heat, which always moves from a warm area to a cooler one.

1) Conduction is heat flow within a material, or, between materials in contact with each other. It is described in terms of "K", the engineering term for the rate of conductance of heat through a material from a warm side to a cool side. K is typically (in the USA) given as BTU per sq ft area, per degree F temp difference, per inch thickness, per hour; be careful when looking things up that the references are using the same units – I’ve found considerable variation, even before getting into metric systems. This is for a single homogeneous material separating the warm and cool regions, which could be either fluids or solids.

"R" value is, more or less, a derivative of “K”, and can be taken as thickness in inches divided by K. “R" is actually a consumer oriented comparison figure, designed for easy comparison by homeowners and such. It is based on tests of actual samples, with varying consideration given to characteristic installation procedures. These factors include such items as inherent air films at surfaces, built-in air gaps as installed, etc. These factors may or may not be mentioned in mass-market literature, although they are specified in various testing standards. While “R” values are usually considered to be additive, it is primarily a measure of conductive insulation, and, convective and radiative effects as discussed below can introduce serious errors in total effective values.

K for most "insulatey" things, like foams and fiber mats, is nearly always very close to 0.25; the best figure I've found is 0.21, for a material that would not suit. So you are really stuck with a best reasonable "R" of 4/inch, or 1 per 1/4 inch, resulting in a practical limit of R2 for 1/2 inch of material - about all you can get in a Magnette roof. It is no good stuffing in more, since the insulating value is almost exclusively a result of captive or "dead" air, not the actual substance of the "insulator". If the insulation is compressed, the K value will approach that of the solid parent material, with R decreasing accordingly - not good.

Air gaps have their own “R” value, which is quite good for dry air, so long as the gap is less than the convection cell limit (see below). In the case of “dead” air, heat transfer is by conduction through the air, not by convection. In a few applications involving sealed gaps, other gases are used instead of air, for lower conductance and hence better performance. Freon was formerly used as a foaming agent in rigid foams, but it eventually escapes, degrading both the insulation and the atmosphere. Argon is used in multipane windows. None of these exotic tricks is of any use in our application. The best “air” gap is a vacuum, as in a Dewar flask or Thermos bottle; in this case both conductivity and convection are zero, but we can’t very well do this in our cars!

2) Convection is the transfer of heat by means of a moving fluid. Properly, the movement of the fluid is caused by density changes due to (conductive) heating at a hot surface and (conductive) cooling at a cool one. This forms what are known as “convection cells”, in which the fluid moves in a circulating pattern, carrying heat from warm to cool regions. Convection cells can be as big as thunderstorms or even larger atmospheric systems; or, they can be quite small. An important point in insulating applications is that a gap of about ¾ in. is the smallest that will support formation of these cells in air; anything less results in “dead” air.

3) Radiation is the transfer of energy by electromagnetic waves through empty space. It is the only means by which energy is transferred from the sun to earth, and is the mechanism for heating of objects exposed to sunlight. The range of electromagnetic waves is called the spectrum, and covers a vast range from very long wavelength low frequencies (radio), to very short wave high frequencies (x-ray). We are concerned with the “middle” of this range. Infrared (IR) is the region of the spectrum immediately below visible light, and is of lower frequency and longer wavelength than visible light. Ultraviolet (UV) is the region immediately above visible, and is of higher frequency and shorter wavelength. All of these behave in much the same way: they travel in straight lines through space, and, are reflected, absorbed or passed by intervening materials. Visible and UV wavelengths are generally transformed to IR when absorbed. This will heat the absorber and the heat will be radiated from the absorber as IR. Absorbed IR behaves likewise, re-radiating from the absorber.

The most important factor in energy transfer by radiation is emissivity or emittance. This number, referred to as “e”, represents the fraction of energy radiated by an object as compared to a theoretical “blackbody”. A blackbody will radiate all of its available energy to a colder body, so e for a blackbody is 1. An object that radiates no energy would have an e of 0. For most substances under most conditions, energy will be absorbed (from a warmer body) at about the same efficiency that it is radiated, so absorptivity can be taken as equal to e. Emissivity is reasonably constant for a given surface at normal temperatures, but can vary a lot at very high or low temperatures. For certain materials, e may have “spikes” at particular temperatures and wavelengths, similar to the “spikes” in transparency discussed below. There is little the layman can do about (or with) this, except to recognize that in some cases, purpose designed insulating materials may have unexpected characteristics similar to those of window tinting films with respect to visible and IR wavelengths. Reflectivity can be taken as the inverse of e and is equal to 1 minus e. This represents energy that is not emitted/absorbed, but turned away or reflected.

E for all real things is somewhere in between the blackbody 1.0 and the perfect reflector 0.0, typically from .98 to .02

It is absolutely essential, and a bit difficult, to understand that emissivity is entirely a characteristic of a surface; it has nothing to do with the underlying material. The base material will affect heat transfer via conduction to and from the surface, but the surface determines the emission (or absorption) of the energy. A consequence of this is that when energy gets to the surface, it will be emitted (or absorbed) to the same degree regardless of whether the energy comes from within the object or from external sources. It is easy to see that visible light is reflected from a mirror surface, and not too much of a jump to imagine that IR might be reflected similarly – in fact placing an electric heater in front of a mirror will demonstrate this. It is considerably harder to understand that IR (heat) conducted through the mirror body (from the back) will be reflected back into the mirror by the same surface, according to that surface’s emissivity.

Anything that causes the IR barrier surface to no longer be the surface will reduce its efficiency. Dust, dirt, paint, glue, oil, etc., will all effectively become the new surface, with e values for those substances, mostly around .95 rather than the .03 or so for a good IR barrier. If the IR barrier is in solid contact with another surface it will be useless, and if it is in loose contact, say with fluffy fiberglass, efficiency will drop a bunch. These points seem to be largely lost on most people, including the suppliers of the barrier materials. For instance, Moss and others who supply the widely available “space age insulation”, say to apply it with the foil side toward the hot surface in an application like under the carpets on the firewall. This would put the foil in contact with the firewall, and invalidate the IR barrier. You would be left with only the conductive (or R) value of the fiber component. In an engine compartment, facing the foil toward the hot engine is good, but the foil soon gets dirty, loosing efficiency, and it is extremely difficult to clean without degrading the mirror finish of the foil.

. From Low-e website: “This pure aluminum facing acts as a radiant barrier on your home, blocking up to 97% of the sun’s radiant energy. This accounts for up to 93% of the summer heat gain in your home. It also keeps the heat in your home in the winter.” (Estimated at 50% vertical up, 85% horizontal, or 95% vertical down reduction in heat loss)
This can be taken as applying to vehicles, as it is just a box in which you wish to control temperatures.

An illustration of radiant barrier effect: My house has a poorly constructed concrete block “foundation”, with many gaps and no insulation. Wind was getting into the crawlspace, making floors very cold. As a quick temporary fix – “it’s freezing in here!” - I wrapped it with Low-e insulation, with the bottom edge following the ground, and the top fastened on the outside of the wall. Since the foundation was from 1 to 3 feet, and I left the Low-e uncut at 4 feet, the insulation extended up the wall by varying amounts. When I went inside, I found that I could “map” the line of the insulation top edge by simply holding my hand a few inches from the wall, passing it vertically up and down. As I passed over the edge line, there was a striking difference between areas covered or not covered by the insulation. To be sure I wasn’t hallucinating, I got my wife to tell me exactly where I had insulated, and she got it precisely. This is through a conventionally constructed wall – ½” plasterboard, vapor barrier, 2x4 studwall with R11 fiberglass, ¾” Celotex sheathing, and aluminum siding – total system value estimated at R18. As it had only been a minute or so since I applied the insulation, the actual wall was still at the temperature it had been, so this effect was entirely the result of IR reflection of my body heat through the wall, off the reflector, and back to me. After the wall had time to get warm, the effect was even more noticeable (although the sharp demarcation was blurred due to conductive effects in the wall), since the now warmer wall was no longer absorbing as much IR from me.

Transparency
Transparency, as we usually think of it, is the property of certain materials, which allows them to not stop the passage of light rays. It turns out that materials may be transparent or opaque to electromagnetic waves of other than visible wavelengths. The fact and degree of transparency depends on the atomic or molecular structure of the material, the precise wavelengths under consideration, and the temperature of the material. For imperfectly transparent materials, which stop some percentage of the waves, the degree of wave blockage will depend on the thickness of the material. Everyday “transparent” materials are unusual, in that they pass a fairly wide continuous range of wavelengths – the visible spectrum and sometimes a bit more, while blocking most other wavelengths. The quality of transparency is more often quite specific as to wavelength, and will typically show several “peaks” of transparency at different wavelengths, or, there may be a transparent range or several, with or without some sharp peaks.
Non-metallic materials can be especially interesting and useful in this regard, and some applications that do involve metals exhibit wave-specific transparency. Leaded crystal glass contains up to about 30% lead; it is almost perfectly transparent to visible light, but blocks x-rays nicely. Some glasses pass visible and IR, some are opaque to visible but almost perfectly transparent to IR, some are the reverse. Most glasses block some UV, and many block most of it. An interesting point is that if a material like a glass is truly transparent to IR, it will allow the IR to pass through without heating the glass at all. Many organic materials are opaque to visible light but almost perfectly transparent to IR and longer wavelengths.
Very thin metal coatings on glass or organic films are frequently used as wave filters The common gold coated welding filter glass is partly transparent to visible light, but blocks almost all IR and UV. Window tinting films are sometimes made with metallic coatings that selectively block IR and UV, but they also usually have a significant effect on visible light, which may not be desirable. It is now possible for non-metallic films to be tailored to block nearly all UV, most IR, and still allow most visible light to pass.

Practical considerations

Thermal:

Given that space is severely limited, one must decide how much to allot to each form of insulation. “R” values of anti-conductive insulation are effectively limited to 4/inch; it is best to get whatever “R” you can without compromising the performance of radiation barriers and air gaps, since radiation is the primary mode of heat gain or loss.

Acoustics:
Sound is a mechanical pressure wave in air for our purposes, mainly, that’s how it gets to your ear. The air is set in motion by vibrating surfaces, which are themselves caused to move by either mechanical vibrations in the works, or by already existing sound waves.

The first line of defense here is to curtail vibration of panels. This is best accomplished by means of either one of the paint-on materials (Dynashield/Quietcoat), or one of the thin composite products (Dynamat “original”, “Xtreme”, or “Dynaplate”). Note that these materials are considerably better performers than tar/bitumen based products, since they have visco-elastic properties – a kind of stiff jelly. As these are somewhat pricey, it is nice to remember that panel vibration is mostly a problem on flattish panels (roof and doors), and it is not necessary to cover the whole panel. 30% coverage damps most of the vibration, and there is not much point in going over 60-70% coverage. A caveat here is that use of one of the aluminum-faced composites will establish a first low-e surface for thermal purposes, so if it proves convenient, you could cover the whole surface, but it is not the cheapest way.

The second line in acoustic defense is to absorb those vibrations that get through line one. This is best done with what is known as a “de-coupled” membrane. A limp and relatively massive membrane is suspended on a very flexible mounting, or between two similar pieces; this is generally a lead loaded vinyl with one or two pieces of very soft foam. This is very efficient and may have some thermal value as well, but it is bulky – usually ¾ to 1 inch thick. I find that it may not have very good long-term durability – see “aging”, below. I feel that this material is overkill in the application, won’t fit properly in many places, and that my suggested scheme below will suffice with lower cost and better durability and thermal performance.

The third line in acoustics is killing sound already bouncing around in the space. In order to accomplish this, the sound waves have to be physically absorbed into surfaces they strike. This means that surfaces must be porous enough for the sound to enter the material, but not so porous that the sound passes straight through to be reflected off another surface and bounced back out. Proper acoustic absorption materials use a mix of open and closed cell foam to do this. In our application, the surfaces under consideration are the interior finish – headliner, door panels, etc. – so we do not have a lot of choice. Magnettes have at least two variations in headliner, a mohair-like fabric, and a fairly smooth surfaced plastic. The fabric is no doubt much better for sound absorption, but the plastic is much easier to keep clean. If plastic materials are used, they should be quite soft and limp, and have little holes in them, with some sort of backing to absorb sound that gets through the holes. A somewhat useful test is to tap the surface with a fingernail – less noise and less sharp noise is better.

Golden rule for sound: NO HOLES! I forget the exact numbers, but in buildings, one square inch of hole transmits as much noise as something like two hundred square feet of typical interior wall. Be sure that all grommets, plugs, cover plates, etc. are in place and sealed! Note that automobile construction sometimes results in “sound pipes”. Cars frequently have, or need, dense foam or felt blocks in things like roof pillars, to keep sound from traveling from one enclosed volume (read resonator) to another. An example would be from boot to roof through the C pillars, or from boot to rear side panels along the wheel arches. These blocks can cause moisture accumulation, leading to rust. The windscreen A posts on BMC 1100/1300 cars have these and do this, as do the frame rails on MGA. Be sure to thoroughly rust proof any areas where they are installed with something self-healing like Waxoyl.

Aging (that’d be the car, not the owner!):
In my experience, plastic foams are quite good for both thermal and acoustic insulation, BUT – they just don’t last very well. I have collected a bunch of samples of these, some being top quality acoustic products similar to the Dynamat foams; after a few years they all disintegrated in my shop. They have not been exposed to direct sunlight, but no doubt have been exposed to a certain amount of noxious fumes from parts cleaning etc. My guess is that these exposures were no more than what would be seen by anything in an automotive installation. While they may last long enough to get past warranty, anyone who pokes around in old cars has no doubt seen a lot of dead foam. Even many of the glues one would use to apply these products will degrade them. Since these applications are mostly in places that are very difficult to access after assembly, I am not inclined to use these products.

The one exception is the polyethylene foam as used in “Low-e” insulation. This stuff seems to be pretty impervious to all known solvents, vapours, and age. It is also of no interest to vermin, does not hold water, and meets all requirements for exposed insulation and vehicle flammability standards. Polyethylene foam is also fairly “limp”, with fair damping, which helps on acoustic problems. A similar product made of foil-faced bubble wrap is also good, but is not as tough, and does not have quite as good acoustic damping. The fingernail test mentioned above gives a much duller and lower sound on the polyethylene foam than on the bubble wrap.

At last, a Plan!
First you need to deal with the acoustic problem of panel vibration. One of the paint-on products, or, something like the Dynamat stick-on sheet products will do. Dynamat “Xtreme” or “Dynaplate” or equivalent will work best for acoustic AND give you a first low-e surface to help with thermal control. Logically you will probably want a paint-on for tricky and complex shapes, and a stick-on for flattish panels. Remember that it is NOT necessary to cover the entire panel for acoustic vibration damping, but maximum coverage is desirable if .you are using this stage as a low-e surface for thermal purposes. If conditions of cost, availability, or ease of installation require, you could use one of the paint-on acoustic products for dampening and as a glue to stick heavy aluminum foil on. Keep the shiny side exposed.

Next, deal with the “sound pipe” problem mentioned above. And, remember that they may also be “heat pipes”.

Third, get some low-e and R value in place. While a single low-e surface would work for a while, they will get dirty and lose efficiency, and one surface gives no R value. So, multiple surfaces with air spaces between are better. In the roof, a layer of aluminum faced Dynamat, and two layers of Low-e or Micro-e loosely suspended should be possible, followed by the headliner. This will give excellent panel damping from the Dynamat, a total of 5 low-e surfaces, two thicknesses of the polyethylene foam, and three airspaces. Total R value should be at least 10 and maybe 15 or better, IR gain or loss should be near zero, and acoustic damping should be excellent. Doors and other large surfaces can be done similarly. It might be best in doors and such to laminate two layers of Low-e with small foam spacer “spots” spaced a few inches apart to preserve the air gaps between layers. In multi-layer situations, it is best if the edges are sealed, so that the middle air gap stays clean, and convection is eliminated from the “dead air” gap. The sealing should be non conductive, so that heat is not transferred by conductance from the foil on one side to the other. Narrow strips of Low-e glued along the edges between the main layers will work nicely.

The rule with insulation, both thermal and acoustic, is that the first bit is always more effective than similar additional material. Each layer takes out some percentage of what it receives, so if it is too difficult to have multiple layers, don’t feel too bad. If possible, allow for redundancy to cover degradation over time. But, always try for some control over each portion of the problem. For acoustic, this means panel vibration, transmission, and surface reflection/absorption. For thermal, IR transmission (e value), conductivity (R value), and convection.

I would highly recommend that you insulate the boot and bonnet as well. You should also do the front and rear bulkheads, but even if this is done, there is little point in having large solar collector ovens and acoustic resonators at either end of your “controlled environment”.

Have a discussion with a knowledgeable and up to date window shop regarding glass film tinting. There are great gains in thermal performance, UV damage reduction, and glare reduction to be had.

I will later tackle the A/C problem, with some suggestions on aerodynamics that should help both A/C cars and standard ones.

Materials Information:
Low-e insulation
http://www.low-e.com/products/products_view.php?Product=Low-E

(The Low-e website is a PITA, at least in Netscape. Printed material is better, though not outstanding, but it comes in a cool “Micro-e” envelope. Product is great. I have it in my house and shop, and some people make vests to go in their hunting clothes, also great inserts in your pants legs and jacket for cold weather motorcycling! I have no interest in this company, but I wish I owned it!) A bonus is that the PE foam is made out of recycled milk jugs.
Product Name: Low-E Insulation
Finished Dimension: 1/4” Thickness _ 10%, 48” Width x 125’ Length, (standard) Shipped in roll form
Core Material: Polyethylene foam
Facings: 99.4% Polished Aluminum with reinforced scrim
Perm Rating: ASTM E-96: 0.008
Flame & Smoke D/S: ASTM E-84-98 Flame Spread: 5 Smoke Developed: 50
R-Value:   *D/S: ASTM C 236: Down 10.74
* D/S:ASTM C 236: Horizontal 7.75
*D/S:ASTM C 236: Up 7.55
*System R-Values as per ASTM C-236, air to air
Emittance: 0.03
*Adjusted to meet criteria equivalent to ASTM 1224

Low-e also makes “Micro-e”, identical to “Low-e” except only 1/8 thick. Effective “R” values are only .25 less than “Low-e”. Good for multi-layer installations.

Foil faced bubble wrap
Widely available, good low-e qualities, not as good as Low-e for acoustic damping.

“Space age insulation”
Widely available, fiber felt about 3/8” thick, with foil on one side. It has good low-e if foil is not in contact with anything and quite good if foil is facing an enclosed space. Reasonable R value in places like under carpet, but the foil is largely ineffective here. Good anti reflective acoustic if felt side is facing the ambient sound, and reasonable anti transmissive if felt is glued or otherwise in solid contact with the panel.

“Space blankets”
Widely available from all sorts of outdoor suppliers and consumer outlets, this is a very thin Mylar film, with an aluminized surface. Cheap, tough, and very compact, it is quite similar to basic window films, and could find use in all manner of multi-layer applications, as an excellent low-e surface and air blocker. It tends to be a little noisy if it flops around.

Dynamat
Not an endorsement of Dynamat, but they do give really good info on their web site, and I value that. There are a number of manufacturers of similar materials.
These materials are primarily for acoustic insulation applications. There are some vague mentions/implications of thermal applications, but it is not really (or accurately) represented as thermal insulation. The foam-based products would be of some thermal value, but note my comments on these foams in “Aging”. Any of these products with aluminum facing would behave as discussed in “Radiation”. You could spend a good deal of time studying Dynamat site; following is my quick appraisal.
http://www.dynamat.com/spec_dynashield.htm - paint on acoustic dampening material

http://www.quietcoat.com - Similar to Dynashield, claim twice as good, half the price, still $60/gal

http://www.dynamat.com/spec_dynamat_original.htm - the original rubbery stuff, good around 50F, falls off above.

http://www.dynamat.com/spec_dynamat_xtreme.htm - Far superior acoustic, aluminum faced. e not given but probably near .03

http://www.dynamat.com/spec_dynaplate.htm - Self stick, high damping adhesive + .010 aluminum .03e; not as good as “xtreme” for acoustic, much better than “original”.

Window Tinting:
My experience with this was long ago, when it was all pretty bad, but things have progressed a bunch. There are now films which claim to be optically clear to visible light, but quite effective at blocking both UV and IR. (Up to 60% IR heat rejection, 99% UV rejection) Space program materials engineering benefits! Apparently many factory installations use these films, so it should stay stuck, even on windup windows. A good shop can evidently put it on compound curved windows; Varitone ought to test their skills! If you pick a film which cuts visible light significantly, beware of local regulations – they vary a lot, and seem subject to a lot of “interpretation” by sundry authorities. 30% reduction seems to be acceptable in most places; many allow up to 70% reduction. Keep in mind the possibility that you may eventually have to sell the car to someone in another jurisdiction.
Good tinting should greatly help the heat/AC problem, as well as protecting that expensive interior from UV destruction.
Since this is a very rapidly developing field, you should do some research and discuss window film technology with a knowledgeable shop when deciding on a film. I found references only a year or so apart which had very different “state of the art” numbers.

General industry info on window tinting (lots more by google –“window tinting”):
http://www.autowindowtinting.com/index.cfm?fuseaction=content.display&pageID=6


This is a preliminary version of this paper, copyright July 2005, Subject to revision.
Please send any comments, questions, or thoughts to:
Fletcher R Millmore, Titusville, Pennsylvania
gofanu@usachoice.net

I am especially interested in how comprehensible readers find it, and any areas that require further explanation. I will incorporate the collective comments into the final version.

I hope you find it of some utility, happy and comfortable motoring!

Addenda:
Modifications:

A major failing of most older cars is a total lack of ventilation with windows closed. This is corrected on newer vehicles, usually by providing air grilles on the lower inside door panels. The air then goes through the door cavity and out similar grilles on the door rear edge, outside of the door shut seals. Some cars, as Rover P6, use the rear roof pillars as vents. There is low pressure along the sides of the car when moving, and high pressure inside from the scuttle intake, so there is some airflow under most conditions. These vents sometimes have open-cell foam filters or screens to keep out mud wasps and other annoyances. This ventilation prevents moisture accumulation from passengers, wet shoes, and tracked-in snow, which leads to window fogging (and ice in winter); anyone who has driven a Mini in winter will probably be familiar with the interior iceberg phenomenon. It is essential for air-conditioned cars and for winter operation with closed windows. If there is no ventilation, there will be NO airflow through the heater or AC evaporator, except on total recirculation settings; in that case, you will run out of oxygen, which is a real threat for a well sealed car; this is believed to be a contributing factor to many cases of “fell asleep at the wheel” and other “inattentive” crashes. Hypoxic stupor may masquerade as terminal stupidity, of which there is an already ample supply. Such vents also help to keep doors from rusting out, a particular trouble on AC cars, where warm external air that gets inside the door will condense on the backside of cold interior panels.
In my Dodge pickup, which does have the door vents, there is still a noticeable improvement in both heat and AC if a window is cracked open. I just installed a small vent fan in a bathroom; with about 32 square inches of free gap under the door, slowing of the fan is still noticeable when the door is closed, indicating continued restriction. There is quite a strong pull on the door when it gets within 4" of the jamb with the fan running. I would estimate this airflow as similar to a good car fan at “normal”, but the car fan has a lot more trouble keeping up than the mains-powered one.
For retrofit purposes, the external door vents can be drilled holes in the bottom of doors, be sure they are outboard of the seals; or, steal some grilles off late model cars to fit the lower back edge of your doors. Inside, there will need to be some modification to door panels; the holes can be covered with a coarse open-weave cloth, as are speaker grilles, for cosmetic reasons. The vents can be inside any door pockets if airflow is not blocked. Look at a few modern cars to get an idea of how large the vents should be. DO NOT be tempted to vent out the rear of the car, or anywhere near the exhaust outlets.

Materials:
Cork is an excellent thermal and acoustic insulation. It is available in several forms as pipe wrap, gasketing, insulation, and floor underlayment. These are compounded with different sorts of binders, frequently rubber-like, which is excellent in cars. I have seen a trowel-on version, but the source escapes me. Industrial refrigeration people may be of assistance.
Stick-on foil faced tape is widely available, Low-e supply it to seal the insulation, and it is commonly used to seal air conditioning and heating ducts. It’s good for piecing in a low-e surface in tight spaces, or for protecting other forms of insulation.
*****
Brian Pollard inquired about this material, thanks, Brian.

Product Description

Thinsulate™ Acoustic Insulation is a hydrophobic polymeric microfiber sound absorber that helps improve interior sound quality and increases thermal efficiency with minimal additional weight.

 

   Two thicknesses (are available):

  • MA4700 Series ~1"
  • MA6700 Series ~2"
     
  • Easily attached with adhesive or staples
  • White, black or metallized surfaces

    The website is extraordinarily uninformative, but big on claims of wonderful things. No numbers are given on anything. There is the clothing sort of Thinsulate, and the “Acoustic”, which is for cars and such. “Acoustic” is a non-woven fiber mat, similar to common fiberglass building insulation. The microfiber material is good in that the fibers are very small, giving lots of attached boundary layer air. This can be taken as “DEAD dead air”, very good and accounting for the claimed 1 ½ times better performance than other similar insulators. It is still essentially an “R” value air trapper. There are vague references to reflecting IR characteristics, helping things along, but again, no numbers. I have a feeling that the microfiber materials may be one of the cases mentioned, where the material is selectively reflective for IR - a very good thing if true, but we don’t know. I recently got a Polartec blanket that is unreasonably warm for its thickness, and have thought that it must be reflecting IR. The metallized surface Thinsulate would be a good IR reflector. I assume from the blurb that it is in fact effective at attenuating transmitted and possibly impinging sound (depending on the surface material), but doubt that it does much for stopping panel vibration.

    The problem with the Thinsulate is that it is not all that thin, for our application. If it has to be compressed, the efficiency of the “R” component will drop, and if the metallized surface is in contact with anything, it will not function correctly as an IR barrier. The internal IR reflection, if it happens, will also diminish to some, possibly small, extent if compressed. The Magnette, like many other smallish cars, has not many places where one or two inches are available for insulation without compression. I consider the dead air gaps bounded by IR barriers to be the most important part of the solution, by far.

  • *****

    Finding Holes:
    A strong light shining and moved around in the engine compartment or boot can help reveal holes if you crawl about inside the car while in a dark garage, or at night. Some sort of strong blower used similarly will work likewise, for those scared of the dark.

    Magnette particulars:
    It’s tricky, but every attempt should be made to insulate the heater blower and its ducting. This stuff can absorb a lot of heat from the engine compartment, which it then blows into the interior. It pretty well invalidates the “cold” air intake on the scuttle.

    Exhaust pipes:
    Heavy gauge stainless pipes will transmit a third to a half the heat of mild steel ones. According to one test I have read, thermal coating the exhaust pipes of a car with 16-gauge stainless headers produced NO additional reduction in heat transferred to the engine compartment, a notable difference over the situation with mild steel pipes. On a Magnette, the proximity of the pipe to bulkhead/floor makes this important, and I’m sure the gearbox would be happier. Also, the stainless pipe will have a much stronger and less troublesome flare at the manifold connection on Magnettes.
    While you’re at it, make the pipes bigger – the Magnette pipe and muffler size is seriously inadequate even for a stock engine. It should be 1 5/8ID-1 ¾ OD for stock engines (60-70hp, this is the stock size for MGB, and is a bit small for that engine; 1 3/4ID-1 7/8OD is ideal.), up to 1 7/8ID-2 OD for 1800 modified (100+hp). If stock Magnette 1 3/8ID-1 ½ OD is taken as 100 %, then these are respectively 140% and 185%. Besides better power and economy, this will also let the engine run cooler at speed. . Note that a too small pipe only interferes with power above the point where restriction gets significant, i.e. at large throttle openings. On a stock Magnette, that means any hill or road speed above about 50mph! A too large pipe may cause some loss of low-end response; so don’t go crazy with pipe size. Carburetters will need needle corrections with this change.

    Heat shields:
    I make heat shields like so: Using highly polished thin aluminum or stainless, cut one piece to size, then cut another about ¼” larger all around. Put a couple of layers of heat insulating paper (now used in place of asbestos) between the metal pieces, and fold the ¼” allowance over the back of the smaller piece. Leave the paper a bit oversize so that it folds around also; this keeps heat from transferring from one metal piece to the other. Trim excess after folding. Mount this on standoffs to give a ¼ to ½ air gap on the backside.
    I once put a 350 Chevrolet engine (with a lot of engine setback) in a Toyota Landcruiser, and insulated the bulkhead around the tight fitting engine as follows. I hammer formed aluminum sheet to the shape of the bulkhead. Then I got the insulating paper wet, and formed it to the bulkhead. After it dried out, I riveted the aluminum to the bulkhead, over the paper, and then polished the aluminum. This worked very well, and almost totally eliminated sound transmission through the bulkhead as well.

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