Dirt can keep animals warm. Fiberglass is in my mom's truck. Fiberglass makes people itch. I have a blanket to sleep with. 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.