One of the highest density foams, 3lb foam is the #1 choice among homeowners and builders alike when high insulation values and strength are the prime concerns; such as with roofing and other similar exterior insulation needs. When cured, 3lb foam provides increased structural integrity, resistance to high winds and other damaging weather conditions, as well as the same water and air resistance you can expect from a polyurethane foam.  As one of the densest foam on the market, it also provides the highest energy savings to homeowners when used to insulate roofs.