Plastics are excellent insulators, meaning they can efficiently trap heat — a quality that can be an advantage in something like a coffee cup sleeve.

How does plastic trap heat?

Polystyrene and plastic foam are both used as insulators as they have small air bubbles trapped inside them. This makes them very good insulators because heat energy can't flow through them. The same idea is used to keep the inside of buildings warm.

Is plastic a good or bad conductor of heat?

Plastics are usually a bad conductor of heat and electricity which means that it cannot conduct electricity or heat when passed through it.