Abstract: Battery separators and the like are produced from non woven mats of thermoplastic fibers which fibers contain an internal wetting agent that is relatively insoluble in battery electrolite and tends to bloom under conditions of use. After preliminary formation the nonwoven mat is heated and then compressed to increase the effectiveness of the wetting agent. The fibers may be formed from polypropylene resin that is treated at unusually high temperatures prior to extrusion and the extrudate attenuated, collected on a drum and compressed to form a preferred separator with small pores and high porosity.