Patent ID: 6872311

Claim:
A filter medium comprising: fibrillated fibers having a Canadian Standard Freeness of less than about 45, said filter medium having performance criteria of: a thickness of less than or equal to about 0.25 millimeters and a Figure of Merit of greater than about 0.075, and an efficiency of greater than about 99.9% when capturing aerosol particles of about 0.18 microns in size and a pressure drop of less than about 40 millimeters water column at a flow rate of about 32 liters/minute through a sample 100 cm 2 in size; and wherein if said filter medium is thinner than 0.25 millimeters, then the efficiency and pressure drop of the thinner filter medium is adjusted to account for a difference in thickness up to 0.25 millimeters thick, to provide a filter medium that meets or exceeds the performance criteria.