The present invention relates to a partially-crystalline copolymer comprising tetrafluoroethylene, hexafluoropropylene in an amount corresponding to hexafluoropropylene index (HFPI) of from about 2.8 to 5.3, and preferably from about 0.2% to 3% by weight of perfluoro(alkyl vinyl ether), said copolymer being polymerized and isolated in the absence of added alkali metal salts, having a melt flow rate of within the range of about 30.+-.3 g/10 min, and having no more than about 50 unstable endgroups/10.sup.6 carbon atoms can be extruded at high speed onto conductor over a broad polymer melt temperature range to give insulated wire of high quality.