Which of these is an example of a heat insulator that contains trapped air?

Woollen clothes are an excellent example of a heat insulator that contains trapped air. The structure of wool fibers creates small pockets of air, which are excellent at reducing heat transfer. Air is a very poor conductor of heat; this property enables wool to trap heat close to the body, keeping us warm in cold conditions.

The unique ability of woollen clothing to retain body heat makes it particularly effective in colder climates. The insulating effect comes from the combination of the wool fibers and the air they hold, which reduces the rate of heat loss from the body. This is a crucial principle in thermal insulation, where materials that can trap air effectively help maintain a stable temperature over time.

Cardboard, aluminum foil, and plastic wrap do not function in the same way. While cardboard can offer some insulation, it does not have the same air-trapping capability as wool. Aluminum foil reflects heat rather than insulating it, and plastic wrap provides minimal insulation without significant heat-trapping capabilities.