... G4 2.DIN 53438-F1,UL900-class2 3.multilayer, 100 centigrade, moisture-proof 4.primary efficiency filter cotton G1 G2 G3 ... G4 DIN 53438-F1,UL900-class2 multilayer 100 centigrade, moisture-proof primary efficiency air filter cotton Use: For coarse ... G2 G3 G4 DIN 53438-F1,UL900-class2 multilayer 100 centigrade, moisture-proof primary efficiency air filter cotton