A process for forming a yarn comprising filaments, each of the filaments comprising a distinct, continuous uniform-density sheath of a first polymer and a distinct, continuous core of a second polymer, with the sheath surrounding the core; the first polymer having a thermal decomposition temperature at least 50 degrees Celsius lower than a thermal decomposition temperature of the second polymer, the process comprising the steps of: a) forming a first polymer solution containing the first polymer in a solvent and a second polymer solution containing the second polymer in the same solvent; the first polymer solution being salt-free and the second polymer solution including at least 4 percent inorganic salt by weight, based on the amount of the salt, the second polymer and the solvent in the second solution, wherein the inorganic salt is selected from chlorides or bromides having cations selected from the group consisting of calcium, lithium, magnesium or aluminum; b) providing a spinneret assembly having separate inlets for the first polymer solution and the second polymer solution and a plurality of exit capillaries for spinning dope filaments; c) forming a plurality of dope filaments having a sheath of the first polymer solution and a core of the second polymer solution by extruding through the exit capillaries a plurality of conjoined streams of the first and the second solutions into a spin cell, d) contacting the dope filaments with heated gas in the spin cell to remove solvent from the dope filaments to form reduced solvent filaments, the heated gas having a temperature such that the dope filaments remain below the thermal decomposition temperature of the first polymer in the spin cell; e) quenching the reduced solvent filaments with an aqueous liquid to cool the filaments, forming a yarn of polymer filaments; and f) further extracting solvent from the yarn of polymer filaments, wherein thermal decomposition temperature of the first and second polymer is determined by a thermal-gravimetric analyzer equipped with a Fourier transform infrared (FTIR) spectrometer as specified in the description. a) forming a first polymer solution containing the first polymer in a solvent and a second polymer solution containing the second polymer in the same solvent; the first polymer solution being salt-free and the second polymer solution including at least 4 percent inorganic salt by weight, based on the amount of the salt, the second polymer and the solvent in the second solution, wherein the inorganic salt is selected from chlorides or bromides having cations selected from the group consisting of calcium, lithium, magnesium or aluminum; the first polymer solution being salt-free and the second polymer solution including at least 4 percent inorganic salt by weight, based on the amount of the salt, the second polymer and the solvent in the second solution, wherein the inorganic salt is selected from chlorides or bromides having cations selected from the group consisting of calcium, lithium, magnesium or aluminum; b) providing a spinneret assembly having separate inlets for the first polymer solution and the second polymer solution and a plurality of exit capillaries for spinning dope filaments; c) forming a plurality of dope filaments having a sheath of the first polymer solution and a core of the second polymer solution by extruding through the exit capillaries a plurality of conjoined streams of the first and the second solutions into a spin cell, d) contacting the dope filaments with heated gas in the spin cell to remove solvent from the dope filaments to form reduced solvent filaments, the heated gas having a temperature such that the dope filaments remain below the thermal decomposition temperature of the first polymer in the spin cell; e) quenching the reduced solvent filaments with an aqueous liquid to cool the filaments, forming a yarn of polymer filaments; and f) further extracting solvent from the yarn of polymer filaments,