They insulate by trapping the air in. Carpets are fluffy so they can trap air. That's why they feel warm. Fiberglass is very itchy, and it insulates in your home. Foam is fun to play with, and it is a good insulator for coolers.
Leaves can make homes for animals.
Snow is cold, but it keeps the ground warm. Plastic is used as an insulator around electrical wires. This keeps the wires from getting hot. Straw is good for birds because it can keep them warm. Fiberglass is used for insulating lots of things like houses.