... total space in the material,so our foam air filter has good permeability,it can filter and deadening effectively the dust in the ... air. The most important is our foam air filter reaches the UL standards,the flame retardant Grades is UL94V0 ... foames comply with ROHS standards. Our pore size of foam air filter:10PPI,15PPI,20PPI,25PPI,30PPI,35PPI,40PPI,45PPI,50PPI,55PPI ...