Lift america s152018 20′ poly web sling eye & eye, 2560/3200/6400 lbs cap polyester web slings are used primarily in conditions where acid is present and minimum stretch is desired. Polyester is unaffected by common acids and bleaching agents, but the material is unsuitable for use in conditions where concentrated sulfuric acid and alkaline is present. Polyester is also unsuitable in locations where temperatures exceed 194f. Stretch of a polyester web sling at rated capacity is approximately 3%.