Unlike rubber thermoset elastomers which can be permanently hardened by heat, thermoplastic insulation will soften and become formable when heat is applied. After being heat extruded (molded), the thermoplastic insulated conductor must pass through a water trough to produce a hard finish to the material. The thermoplastic insulation will soften again if exposed to excessive heat or open flame. If enough heat is applied, the material will become so soft it will flow like melted candle wax.