K FILTER Polyurethane (PU) pleated filter bags provide a modern composition that can be easily modernized in existing dust collectors. These bags have a flexible PU top and bottom and the bags are inserted in the system as a âtop loaderâ. A metal plug is provided with each bag that is to be inserted inside the PU top. The PU expands because of the metal plug and seals the bag at the plate. Owing to the mechanical properties of PU, these bags have a max temperature limitation of 90°C