Patent ID: 8900351

Claim:
A filter medium, comprising: a porous polytetrafluoroethylene (PTFE) membrane; and a gas-permeable supporting member for supporting the porous membrane, the porous membrane and the gas-permeable supporting member being integrated, wherein the gas-permeable supporting member includes: a substrate having gas-permeability, wherein the substrate is composed of fibers; and a fiber layer that is placed on the substrate so as to be in contact with the porous membrane, wherein fibers that compose the fiber layer have a smaller average fiber diameter than that of fibers that compose the substrate, the gas-permeable supporting member has a structure in which fibers of the fiber layer enter into the substrate and are entangled with the substrate so that the fiber layer is bonded to the substrate, and the fiber layer contains polyolefin-containing fibers that are bonded to the porous membrane.