Insulation is a thermal barrier as it stops or slows down the movement of heat through convection (movement through air) and conduction (movement through contact).
During the winter, your insulation prevents the heat inside your home from escaping to outside, which makes it much easier to keep your house warm and energy efficient.
But it also works the other way around. It the summertime, insulation in the walls and especially in the attic prevent heat from the outside entering your home. This lifts a major burden on your air conditioning system.
How much of a difference will proper insulation make during the summer?
Lets look at the attic for example. Because this spot has poor ventilation and receives heat from the sun beating down on the roof, the temperature in the attic on hot days can exceed 130°F. Without proper insulation in the attic, that heat can and will seep down into the house, which can result in a climb in temperature of approximately 10°F. That’s often the difference whether you keep your AC on or off.
The U.S. Department of Energy estimates that you could save at least 20% off your air conditioning bills if you properly seal up the insulation leaks in your home.