They are bags sewn in the form of a bag and are used for the separation of dust from the air flow. They are generally manufactured in needle punched felt, with triple stitching or temperature gluing. The filter bags are supplied in the material selected according to the requirements of the process to be decontaminated and in the dimensions required; they are manufactured under strict quality standards. At the bottom they have a textile disc and a double fabric reinforcement to avoid breakage due to friction, at the mouth they have a steel strap, which when expanded makes a seal on the bag holder sheet. This is why this type of sleeve is called self-fixing or fixing (Snap Band). The sleeve is manufactured lengthwise with a triple seam, in thread of the same material.