... Acid-resistant,alkalifast 4) Flexible,good tensile 20ppi Mesh Foam/Filter Sponge detail:1)Material: PU (polyurethane)2)Aperture: from ... to 60ppi is available3)Open porosity: >98%4)Shape: square, column etc5)Different hardness and basic color is ok6)Advantage ... , reusable,washable, acid-resistant,alkalifast, Flexible,good tensile7)Use: filter dust, air, liquid, equipment filter etc 20ppi Filter Foam