People insulate houses with styrofoam and fiberglass. Styrofoam cups keep hot chocolate warm. Straw is made of grass, and some people use it to keep their home warmer. Cardboard is another insulator. It helps ice cream stay cold.
Leaves are a good insulator.
Squirrels use leaves to make their home. Wood chips trap air and can be used to insulate. It blocks the heat by absorbing it into it's many layers of fabric. Another insulator is copper. Copper blocks electricity because the electricity can't get through the layers of minerals.