Pura PC Computer Air Filter - Polyurethane Foam Filter 1 sq ft 60 pores per inch (ppi) polyurethane foam Can be cut to fit any shape(s) and size intake(s). Different mounting options of inside or outside the computer case to retain form and function. Minimal airflow resistance and collects all kinds of dust and dirt - pollen, pet dander, lint, etc. Washable; just rinse under tap water.