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

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

In: Physics
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I heard that the heat of the dryer is not what causes the shrinking so much as the tumbling action of the dryer. And things like plastic and especially styrofoam are products that have expanded and so added heat breaks them back down into what they are made from.

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.

Heat gives energy. It gives the energy to expand by forcing atoms to move around more freely and it also breaks atomic bonds.

Remember that clothes are woven together. It’s like a mesh of wool or cotton held closely together, but there’s room for air to pass through. I assume that as you heat it, this can give atoms energy, expand the fibers, making the empty in-between space shrink. (Just looked this up, seems the tumbling aspect of a dryer is more responsible for the constriction).

Same with plastics and polystyrene: they’re woven together as polymers (“bundles”) of molecules, with a bit of empty space between them. When we have a solid forming with that empty space, that’s crystallization… Same way water molecules can crystallize to make a less-dense solid (ice). Heating it up breaks those bonds, making it shrivel and lose volume as it melts and reverts to liquid.