The latest. Sales from http://www.daytonimports.com emailed me to let me know that there IM heat shield gasket is 100% phenolic. Link to product on Ebay here (http://cgi.ebay.com/ebaymotors/ws/eB...spagename=WDVW)
This would seem promising, as this is the same material as other quality IM heat shield gaskets. I could not find any additional information on their website for this product.

The following information regarding the thermal conductivity of a phenolic heat shield is from Outlaw Engineering which makes a similar product.

"ThermoBlok spacers are made from a laminated phenolic composite with a thermal conductivity of 0.29 W/m*K. Aluminum on the other hand has a thermal conductivity of 150 W/m*K, more than 500 times higher. You must also remember that there is a gasket, commonly steel (20 W/m*K thermal conductivity), placed between the manifold and head. Replacing the 0.025" thick steel gasket with a .250" ThermoBlok thick spacer will conduct an amazing 688 times less heat (yes, that's nearly 70,000% reduction!).

The ThermoBlok spacer material also exhibits high stiffness and compressive strength, can withstand temperatures up to nearly 300°F, and has a thermal expansion coefficient very similar to aluminum to increase sealing capabilities."

[NEW RELATED QUESTION] - If the stock gasket is .025 and the heat shield gasket is .250 will I need longer studs for my 91 Teg LS B18A? Should I just go with bolts?