Installing rigid insulation under new siding is like putting a neoprene sleeve on your beverage during the summer; it keeps heat from the outdoors from getting in and warming up the inside. This will lowering your energy bills in the summer as well as the winter.

In hot weather, your air conditioner must work extremely hard to keep the inside of your home cool. The harder your air conditioner works, the more expensive your energy bills become. Not only is your home surrounded by heat, but that heat may also be forcing it’s way into your home through a process called "thermal bridging".

Thermal bridging is the movement of heat through the side walls of your home. Heat bypasses the fiberglass batt insulation (pink stuff) in your wall cavity and moves across the wooden studs. Heat always moves towards cold, so during the summer, heat is transferring through your walls from the warm outside to the cool interior of your home.

The United States Department of Energy seems to agree. They say that "When new siding is to be installed, it’s a good idea to consider adding thermal insulation under new siding."