Initial air filters come in four styles: plate, folding, bag, and box types. The frame materials include paper frames, aluminum alloy frames, galvanized iron frames, and stainless steel frames. The filtering materials consist of non-woven fabric, nylon mesh, activated carbon filter cotton, and metal mesh. The protective mesh options are double-sided painted wire mesh and double-sided galvanized wire mesh. They are cost-effective, lightweight, versatile, and have a compact structure.