Air is a good insulator because its molecules are very far apart. This makes it difficult to transfer heat, according to Dr. Ken Mellendorf, a physics professor at Illinois Central College.
Heat typically flows from warmer spaces to cooler spaces via radiation, conduction and convection. Because air molecules are so far apart, still air limits conduction and eliminates convection, which is the transfer of heat by the movement of a fluid. Fiberglass and cellulose are two other types of insulation that limit air flow and prevent heat transfer. Insulating a home saves money and reduces the amount of natural resources used for heating and cooling.