Polypropylene filter bags can be divided into short polypropylene fiber and long polypropylene fiber.The yarns which are made of long polypropylene fiber are very slippery. So the bursting strength and gas permeability of the long polypropylene are much better than that of the short poly-filter cloth.The surface of industry filter-cloth which are made of polypropylene fiber is very smooth. So it is suitable for powder filtering. Moreover, the products which we has just developed is the best filtration material for the fields of chemical and medicine,but it is not suitable  for power filtration.The products of 4212 which are made of short polypropylene fiber,so it is the best filtration material for the dyestuff factory,the effect of acid spotting and gas permeability are as far times as 120-170 of polyester, so it can speed up the velocity of  filtration,and also avoid walling up draff