I was thinking about trying out making a prop destiny gun from extruded polystyrene since I have some. My question is will that react badly if I try to mold it with silicone? Id hate to spend hours working on it only for it to melt or something. Thanks in advance!
anything with sulfur is bad for silicone molds...most things other then that i don't think you'll have a problem.
if however your surface is porous you may need to seal it with something before pouring the mold.