As far as I knew, the material controls:
-the sound of breakage,
-the sound of the gibs hitting the ground,
-which gibs it has,
-the transparency of the gibs. e.g, using the material "glass", but using the "catwalkgibs.mdl" gibs will make the catwalk gibs look transparent (along with the rest of these),
-the decal of the hit.