We manufacture our own line of Electrostatic Air Filters. Our filters utilize an all aluminum .032 frame construction, with one 1" layer of Blue/White Polyester a layer of clear polypropelene and one layer of white woven polypropelene imbedded with the ViBax 50 antimicrobial. This material inhibits the growth of viruses, mold spores and other particulate. We custom make all sizes. If your size is not listed, Please call Toll Free at 1-888-242-7725. We make our filters nominal or actual. Nominal is 1/4" less than needed for ease of installation. We are quite proud of these filters and you will be too. With proper maitenance they will give you years of enjoyment of cleaner air.