Replacement OEM air filter from Stihl. Keep your chainsaw running efficiently with a clean air filter. This is a heavy duty (HD2) cartridge type air filter, which does a great job of filtering large volumes of air. The pleated surface has a fleece material that filters very well (which is a good thing), but tends to ice up in sub freezing conditions. We recommend a nylon mesh version of this filter for frozen sawing conditions. Eventually, the smaller filter pores will clog up with sawdust and your chainsaw will begin to struggle for air flow.