Believe it or not, plain old wood (oak or teak) is a better heatshield material than tungsten or asbestos. For a high heat flux entry, the material properites that you want are "ablation" and low heat conduction. What's ablation? An ablating heat shield material outgasses when it gets heated. The idea is the heat shield material gets heated by shockwave heated atmospheric gas. The heat shield material then out gasses and blows the hot hypersonic gas away from the heat shield's surface. This is a variation of the old camping trick of boiling water in a paper cup placed in a camp fire. The heat absorbed by vaporization of the boiling water keeps the paper from reaching its ignition temperature. So long as there is water in the cup, the paper won't burn. Wood also has the nice property of having low heat conduction. The Chinese used teak for their reentry capsules. I believe Lockheed-Martin used maple for the the nosecones on the D-5 SLBM. The main heatshield material used on all American Mars landers is SLA-561V. The prime ingredient in SLA-561V is cork dust. I'm convinced that balsa wood would work just as well as SLA-561V and cost a hundred times less. However convincing people to use balsa wood to protect a quarter billion dollar spacecraft can't pass the giggle test so we stick with SLA-561V.

Gary