Does plastic expand at colder temperatures?

Question

After placing a dry solid block of nonporous plastic material in the freezer for a while, I was surprised to find out when I retrieved it that it had expanded globally by a few inches. Which type of plastic must this be and do plastics expand at colder temperatures?

Is the plastic material a solid block or a structure? Is it porous? What else was present? Was it wet? — Chemomechanics, Nov 05 '20 at 23:38

score 1 · Accepted Answer · answered Nov 05 '20 at 23:26

Materials with a negative thermal expansion (NTE) coefficient will increase in size as they are cooled down. Not all plastics have a NTE, but it is not a property seen only in one specific type of plastic. I don't think the plastic can be identified only knowing that it has a NTE.

Does plastic expand at colder temperatures?

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