... ) Acid-resistant,alkalifast 4) Flexible,good tensile 20ppi Mesh Foam/Filter Sponge detail:1)Material: PU (polyurethane)2)Aperture: from 10ppi to ... function, reusable,washable, acid-resistant,alkalifast, Flexible,good tensile7)Use: filter dust, air, liquid, equipment filter etc 20ppi Filter Foam