The extended surface air filters are mainly as the medium filter before HEPA filters, catch 0.5-1 micron fine dust, reduce the burden of HEPA filters, increase the final stage filters life. Extended surface air filters efficiency is almost about F7 or F8, other efficiency F5, F6, F9 available. The filter media is synthetic or glass fiber. Filter media are pleated designs to maximize the filter area. Synthetic filter media and glass fiber media are with large dust holding ability that is perfect to collect dust, the long fiber is created with electrostatic adsorption ability that is very helpful for capturing dust. The fluffy construction can give more space for dust holding.