Our inverted bag units have a permanent filter. This special Surf-Tex™ filter resists bacteria, mold, and mildew growth. This material can also capture particles as small as .3 microns and has a dust retention of 97% efficiency. The inverted bag units have a convenient utility valve on the unit. The debris is collected in the bottom canister. This canister features our patented air channel that allows the bottom canister to have a liner. This makes emptying the debris a breeze.