It's All About Air Tightness

One of the major factors in achieving top energy efficiency is airtightness. "Consider an airplane," says Richard Rue CEO of Energy Wise Structures. "When flying at 35,000 feet, the plane is exposed to outside air temperatures of -50 F, with wind chills as low as -150 F. The shell of a plane is typically just 2 inches thick, but passengers don't freeze because its airtight. Once a structure is airtight, it takes very little energy to keep it at a certain temperature."
Thats why Rue often recommends the use of spray foam insulation in exterior wall systems. "About 80% of all air leakage through a house is through the walls," says Rue, "and spray foam insulation eliminate that leakage."

Because spray foam insulation completely encapsulate the structure, it provide a continuous barrier against air infiltration. The walls also have a high thermal mass, which shields the home interior from outdoor temperature extremes, reducing peak and total heating and cooling needs.