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 Festool CT 36 dust extractor continues to deliver full suction until the bag is virtually completely full. Other manufacturers feet bags do not counter this caking effect and suction is reduced dramatically throughout the use of the bag, often resulting in a situation where suction is lost before the bag is completely full.