Your attic can get extremely hot and cold. If you have attic air leaks and insufficient insulation, a lot of your conditioned air will escape into your attic and out of your roof. Additionally, lack of insulation means more hot and cold temperatures seeping into the home.
When temperatures start climbing, the hot rays from the sun beam down on your roof. As the roof absorbs heat from the sun, it starts to heat up your attic like an oven. Proper insulation in the form of radiant barriers will drastically reduce the rate of heat transfer.
Reflective, radiant-barrier insulation is usually made of aluminum foil with a variety of different backings, including plastic film and cardboard.
This type of insulation is most effective in warmer climates but can also be used for comfort and energy savings in cold weather. The radiant-barrier insulation is attached to roof rafters, floor joists, and wall studs to reduce radiant heat flow, mostly from the outside in, but also from the inside out.