In a typical home, up to 20 percent of air that moves through the duct system is lost to leaks, which leads to higher utility bills. Ducts are often found in walls, ceilings, attics and basements, and duct sealants help to make your home more energy efficient and comfortable. As an energy saving product, duct sealant and air duct insulation can lead to lower utility bills by prohibiting the leakage of tempered air in your home. Mastic fibrous adhesive sealant is a sealant that is highly resistant to the elements and can be used indoors or outdoors. Duct sealing can be done as a DIY project, but many homeowners opt to hire a professional.