Bgears Fan Filter 90mm 2 Pieces Pack. Fan filter is design to mount on the fan as a fan guard to protect and prevent dust from entering into the Computer system and to prolong the lifespan and performance of a fan by preventing the dust from clogging the fan blades and the fan motor. Each Bears Fan Filter consist of 3 parts; Top Filter cover, Washable Filter, Bottom Filter cover. Each Pack consist of 2 pieces of Fan Filter.