One of the energy-efficiency measures recommended by the EPA is sealing of air ducts to prevent air leaks. This is often known as a duct seal or duct sealant. When you hire a duct-cleaning service, they may recommend a different kind of duct sealant. This type is designed to coat and protect your ductwork against mold and bacteria. This is sometimes called "encapsulation" and while this may sound good, according to the EPA, there is no evidence that such a sealant actually works to protect against mold or bacteria growth in home or office ductwork. New studies are conducted in many areas, and some companies may claim that their products are "the latest thing". If your duct-cleaning service wants you to consider a duct-sealing product, ask plenty of questions and find out what potential health effects could arise from having such chemicals placed into your ventilation system. If you can't get sufficient answers your questions, avoid the duct sealing procedure.