Polyester is a long chain synthetic polymer composed of at least 85% by weight of an ester of a substituted aromatic carboxylic acid, including but not limited to substituted terephthalate units and to units of parasubstitutedhydroxybenzoate. It is sometimes know under it's trade names as Dacron (Dupont) or Terylene. Polyester is very close in appearance to Nylon, and is differentiated mainly by the fact that it does not stretch as much. This limits it's ability to absord shock loads, approximately 60% of the capacity of Nylon ropes. It's advantage is less stretch at working loads, approximately 5%, allowing for reduced head room during lifting. Like Nylon ropes, Polyester ropes need to be set when brand new, and will permanently stretch by approximately 6% under the maximum working load. Unlike nylon, polyester does not absorb water, and hence will not loose strength when wet.
Like nylon it has very good resistance to ultraviolet, though prolonged exposure will cause some loss of strength. It has excellent abrasion resistance, especially when wet. Polyester has good resistance to most mineral acids, though it will decompose in concentrated solutions of sulfuric acid. It has moderate resistance to strong alkalis at room temperature, with decreasing resistance with increasing temperature of the alkali solution. It has excellent resistance to bleaches, and other oxizidizing agents. Polyester has slightly lower strength to weight ratio than Nylon. Typical tenacities are in the 8 (gpd) range, some newer grades approach 10 (gpd). Polyester yarns are solution dyed and available in a variety of colours.