Basics

Essentially charcoal made from a airated/pourous material
Anything from bread, to a celluloistic purpose made lattice, selected types of wood, machined wood, purpose formulated polymers, or a chemical reaction like those used in "Black Snake Fireworks" can be used as a source material
Useful as an insulator or ablative material, may also have use as an electrode? need to test conductivity, but the high surface area would be useful, may make good substrate perhaps?
Can also be used as a refractory material, although it ablates and thus falls apeart after long term use
Precarbonisation is useful, but the core material doesn't neccisarily need to be
It also, due to insulation and ablation, cools very quickly
addition of baking soda also adds a useful effect according to nighthawkinflight's youtube video
China Has Used Wooden Heat Shields for Atmospheric Reentry with their FSW Satellites using White Oak Wood, this wasn't precarbonised, or highly foamed, but uses a similar method

Carbon Foam