Why doesn’t a dishwasher dry plastic?

After a dishwasher cycle, the plates and glasses are usually dry, whereas plastic boxes and cups remain wet. The difference is due to the different materials’ ability to absorb heat, also known as heat capacity.

Porcelain, glasses and cutlery have a much higher heat capacity than does plastic, while glasses, porcelain, and cutlery generally also consist of thicker materials than plastic, and can hence contain much more heat.

Plastic is also a relatively poor heat conductor and so the thermal energy is not passed effectively to the surface. Porcelain, stainless steel and glass are good at conducting heat, so they can make the last water evaporate from the surface.

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