What does caulk do anyway?

from,JK2

Caulk is a basic texture which you use to make brushes with. When you use caulk is saves alot of space in your map because the game engine ignores it so if you texture over a caulk brush you are saving space rather than making a brush from the texture. Many mappers make their maps in caulk to start with and I find it much easier too work with.

It appear solid but invisible in game, its used for building structures so the game doesnt have to draw faces which are not seen yet still required to be solid.