If heat makes things expand/less dense, why does heat make clothes shrink and thinks like plastic and styrofoam shrivel up?

Question

If heat makes things expand/less dense, why does heat make clothes shrink and thinks like plastic and styrofoam shrivel up?

In: Physics

Answer 1

Something like foam shrinks when heated because it is melting. Before melting it should expand a bit just like everything else. Foam is not solid, it is porous (full of holes), and when it melts those holes close making it take up less space. The fibers in clothing probably do something similar.