Patent ID: 8137436

Claim:
A humidifier membrane comprising: polyolefin fibrils forming a microporous web with a plurality of pores, wherein an average pore size is 0.05 μm to 0.4 μm as established by a PMI Capillary Flow Porometer; and a hydrophilic surface arranged at a surface of the fibrils, wherein the humidifier membrane has a Gurley number above about 300 s/50 ml at 23° C. and 50% RH, and a transfer rate of water through the humidifier membrane above about 400 (g*mm)/(m 2 *day) at 70° C. from a first gas having a relative humidity of 100% on a first side of the humidifier membrane to a second gas having a relative humidity of 50% at a second side of the humidifier membrane for passive transfer of water.