As time progressed, however, so did duct-cleaning methods. Encapsulation became the new trend. This method required duct cleaners to spray a sticky substance into the ductwork, effectively gluing contaminants in place. The theory held that once a particulate or object was glued in place, it could no longer travel through the ductwork and contaminate the system.
Consumers didn't appreciate this idea, though, and it was abandoned as the National Air Duct Cleaners Association (NADCA) began requiring source removal from duct cleaners, mandating a clean and contaminant-free system.