Prompted by a discussion on another board I thought to solicit your opinions and what you believe is the best material to insulate the cabin against the heat coming from the engine compartment and through the tunnel.
While researching material that could be used as a backing for the firewall pads I looked at quite a number of products and tried to find some hard facts behind some of the claims. Specifically what I was looking for were data on either thermal conductivity or thermal resistance of the material.
First a little bit of background.
In the USA here most of us are familiar with the "R-value" of insulating material in the construction or home appliance business. The R-value is a measure of thermal resistance and is the ratio of the temperature difference across an insulator and the heat flux (heat transfer per unit area):
http://en.wikipedia.org/wiki/R-value_%28insulation%29Note that the standard R-value is expressed as "per inch" thickness and often it is not clear whether the stated R-value in a spec sheet is the standard value or the actual one taking a different thickness into account.
Another consideration is the ability of a material to reflect radiant heat. For example, the heat in the tunnel arrives there mostly by radiation through the air and not by direct contact between metal surfaces. Radiant heat is predominantly infrared radiation and some materials, for example, anodized aluminum is claimed reflect about 50-60% of radiant heat but does not give off heat. That is the reason why there are aluminum heat shields between the manifolds and above the exhaust pipes. Some insulating materials incorporate a thin aluminum foil but to be effective it needs to be facing the heat source. These sheets should always be attached or glued directly to the chassis without an intermediate an intermediate layer. Dynamite, a sound barrier, is installed with the foil facing into the cabin; such an arrangement is not a good solution because the reflected heat is now trapped in the black polymer layer.
Here are some materials for which I could find specific information:
Thermozite: specific R= 1.3 (standard R= 3.7) {
http://www.perfectfit.com/15269/154086/Carpet--Padding/Thermozite.html} Price: ~$1/sq.ft.
KOOLMAT: standard R=1.65 {
http://www.koolmat.com/what.shtml} Price: $14/sq.ft.
EZ Cool Insulation: specific R= 1.6 {
http://lobucrod.com/} Price: ~$0.68/sq.ft. -
I am not so sure about the claimed R-values and the material collapses easily.VB-3 with lead septum: specific R= 1 (standard R = 4) {
http://cascadeaudio.com/car_noise_control/car_barriers.htm} Price: ~$17/sq.ft.
VB-4 barrier: specific R= 1 (standard R = 4) {
http://cascadeaudio.com/car_noise_control/car_barriers.htm} Price: ~$8/sq.ft.
These values are in general agreement with the tabulated information for polymers provided in the Wikipedia article.
Please add you own favorite material or any other comments.
