Cooler air is denser and will sink. The rising and falling air gives rise to convection currents that move heat. Conduction and convection require that objects be in direct contact for heat to be transferred As you sit in front of your fireplace during a cold winter night, you can feel the heat of the fire. The heat of the fire is transferred by waves you cannot see. The waves are called electromagnetic waves.
Radiation is heat transferred through electromagnetic energy.
Food at fast-food restaurants is kept warm by heat lamps that radiate heat to the food. Many materials can slow the transfer of heat though conduction or convection. Air is an excellent insulator. When you dress in layers during a cold winter day, it is the trapped air between your clothing that acts as an insulator. Radiation can be controlled by smoothness or the color of a surface.