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. Styrofoam is used to insulate in coolers, walls, attics, and basements.
Dirt is a good insulator for ants and worms.
Some people put snow against their house because it keeps it warmer. Carpet is an insulator because it keeps the cold out. The thicker it is the warmer it is. Leaves can be insulators for animals to keep them warm. Leaves can keep seeds from dying.