The CT SYS Portable Dust Extractor replacement bags feature a self-cleaning filter bag that solves a problem that plagues other dust extractors and vacuums. During normal use, fine particles of dust cling to the inner lining of the filter bag resulting in caking. This coating of dust lowers the effective suction power dramatically resulting in poor extraction efficiency and performance. Caking can also cause additional strain on your dust extractor's motor and contribute to premature failure. Festool has addressed this issue by developing a unique pliable fleece filter bag. Because the bag is not rigid like many other types of bags, such as paper bags, it prevents caking. This means that your dust extractor continues to deliver full suction until the bag is virtually completely full.