Insulation slows or prevents heat, sound, electricity, mechanical vibration or radiation from coming through walls. There are four types of insulation: heat insulation, sound and vibration insulation, electrical insulation, and radiation insulation.

Heat flows from warmer to cooler areas until there is not a difference between the two temperatures. Heat insulation is used to delay the flow of heat for human comfort and survival and to prevent freezing damage to different objects. Heat flow involves three mechanisms. Conduction is how heat moves through materials, and convection is how heat circulates through gases and liquids. Radiant heat moves in a straight line heating anything in its path. Most insulation materials slow down conductive and convective heat flows. Radiant barriers reduce radiant heat gain.