Abstract: The invention provides a process for making polyamide fiber with high molecular weight and/or chemical and thermal resistance using conventional single or twin screw extruders. The process includes melt-blending polyamide polymer comprising at least about 75% by weight of poly(hexamethylene adipamide) or poly(.epsilon.-caproamide) and having a formic acid relative viscosity of about 20 to about 50 with a polyamide additive concentrate comprising polyamide polymer and an additive selected from the class consisting of stabilizers, catalysts and mixtures thereof to form a molten polymer which contains about 0.05 to about 2 weight % of the additive and extruding the molten polymer from a spinneret and forming a fiber having a denier per filament of 1 to 40. Fibers made by this process have great utility in the batt of papermaking machine felts where they provide improved resistance to wear and/or chemical attack.