Battery separators and the like are produced from nonwoven mats of plastic fibers which fibers contain an internal surfactant that is soluble in the molten polymer but insoluble in the cooled polymer and tends to bloom under conditions of use. A second surfactant is coated on the exterior of the fiber. After preliminary formation the nonwoven mat is heated and then compressed to increase the effectiveness of the internal surfactant in cooperation with the coated on surfactant. 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.