The type designation on the wire will indicate if the insulation and jacket are thermoplastic or thermoset. If there is a “T” like SVT or SJT the material is thermoplastic. If the “T” is not present, like SV or SJ, the jacket and insulation are thermoset. Another type material, thermoplastic elastomer, is a special case and will be discussed another time. Cords have been made with vinyl plastic (PVC) for about 70 years. PVC is an ideal material to use for extrusion and molding because of its low cost, easy processing capability, and good electrical properties. Newer cords are made without lead to meet Prop 65 and RoHS. PVC is thermoplastic and that means it will melt at approximately 350°F when touched with a hot object or flame. This is true regardless of the temperature rating marked on the cord jacket. PVC also has limited use in very cold temperatures because it gets stiffer as the temperature gets lower. The practical low limit on ordinary cords is -20°C (-4°F). Thermoplastic is a good general purpose material but in certain applications thermoset rubber must be used. Those situations are when the cord is attached to an appliance with a heating element that can easily contact it. Irons and some space heaters are good examples of use for a thermoset cord. Thermoset materials have the same temperature ratings as PVC, 60°C or 105°C.