Polypropylene fibers have a softening point in the region of 140°C and a melting point at 165°C. At temperatures of -70°C or lower, PP fibers retain their excellent flexibility. At higher temperature (but below 120°C) PP fibers nearly remain their normal mechanical properties. PP fibers have the lowest thermal conductivity of all commercial fibers. In this respect, it is the warmest fiber of all. The thermal conductivity of common textile fibers is shown in the following Table.