%CompileNonSolid
Add this VMT parameter to make brushes non-solid. When compiling the map, VBSP will flag the brush with this material as non-solid. Useful for foliage or light effects.
Unlike a brush tied to a func_illusionary, a worldspawn (or func_detail) brush with %CompileNonSolid
does not count as an edict.

%CompileNoDraw
in 



(BSP requires all sides of a brush to either have or not have collision, due to how clipnodes work.)