A passive humidifier membrane is provided. The humidifier membrane consists substantially of polyalkene with a plurality of pores, wherein the average pore size of the plurality of pores is 0.05µm to 0.4µm as established by a PMI Capillary Flow Porometer. The humidifier membrane is virtually airtight while providing a high transfer rate of water. Transfer of heat is also high. The humidifier membrane is particularly suitable for heat exchange and water transfer between fluids and it is highly advantageous for applications inside or outside fuel cells such as PEMFC. The membrane is also particularly advantageous in the application as humidifier for air or oxygen.
