PERLON (Plastic Polymer) Patented by the Mfg. Can be stretched, but goes back to original diameter. Perlon can be stretched 400 to 600 times before loosing tensile strength. Once other monofilaments lines on the market are stretched, they do not go back to original diameter, thus, the tensile strength is depleted. Rating: About 10% on the plus side. In other words, 10 lb test should break at about 11 to 12 pounds. Use: Fresh & saltwater, spin & casting reels.