Patent ID: 8465565

Claim:
A gas filtration media, comprising a multilayered polyethylene membrane having a particle filtration, PF, value calculated according to the formula: PF=(-log(Penetration (%)/100)/Pressure loss (mm H 2 O))×100 in which the Penetration (%)=100-Collection efficiency at a Pressure loss (unit: mm H 2 O) measured when air is flowing through the membrane at a flow velocity of 5.3 cm/second and a collection efficiency (unit: %) measured using dioctyl phthalate having a particle size of 0.3 μm (U.S. Military Standard MIL-STD-282 (1956)), the PF value of the membrane is at least 20, and wherein the membrane has a porosity of at least 88 vol-%, a thickness of greater than 10 μm to less than 200 μm, and an average pore size of at least 0.5 μm, wherein the polyethylene is stretched in a transverse directions by a factor of at least 10 times the area and in the machine direction alone is stretched by a factor of at least 2.5 times the area.