Why Doesn’t Plastic Dry as Easily as Glass in the Dishwasher?

An Abstract reader recently sent me this question: “Why doesn’t plastic dry in the dishwasher? Or why doesn’t it dry as quickly/easily as glass? This drives me totally nuts.” Good question! That phenomenon drives me nuts too.

The answer appears to have a lot to do with the amount of energy (in the form of heat) that different sorts of tableware are able to absorb.

Ounce for ounce, plastics (such as children’s sippy cups) may be able to hold more heat than glassware or ceramic bowls. However, cups and plates made from ceramic and glass are denser and have more mass (i.e., they are heavier) than those made from plastic. This increased mass allows glassware and ceramics to absorb and hold more energy (heat) in the dishwasher – so they stay hot longer than plasticware. That’s why ceramic plates are usually hotter than plastic ones when you unload the dishwasher.

The fact that glasses and ceramics stay hotter for longer has two effects: first, water is more likely to condense on plastics (or at least not evaporate), because they have a cooler surface; second, any water on the hotter glass and ceramic surfaces is more likely to evaporate.

If you have any additional questions for the Abstract to answer, let us know in the comments!

Note: Many thanks to Dr. Doug Irving, assistant professor of materials science and engineering at NC State, for taking the time to talk with me about this subject. Any errors in the above post are mine alone.