What is the essential difference in the composition of PICA compared to the pure silica material of the HRSI tiles?

Answer

PICA uses a carbon fiber structure impregnated with a phenolic resin.

PICA consists of a carbon fiber structure that is impregnated with a phenolic resin, differentiating it from the silica fiber composition of the HRSI tiles.

What is the essential difference in the composition of PICA compared to the pure silica material of the HRSI tiles?
AerospaceMaterialspacecraftreentryheat shield