Heat shield tiles are an important part of the space shuttle. I think the base mod uses stone brick to represent them, but they should be switched out. Though maybe not at a 1-1 ratio. There should be a similar number of Low density structures as there are heat shielding tiles.

I think that replacing the heat shielding tiles makes some sense when refurbishing though.

EDIT
Ah, I see now that it's done conditionally on angels mod, nevermind.

Heat shield tiles from Bob's Revamp mod should be used if the mod is installed and the option is ticked.