Hemp, being inferior in strength, stretch and rot resistence to the new polymers such as nylon, polyester and polypropylene, was quickly discared. Although Polypropelene is not as strong as nylon it is in fact lighter. It is also stiff, very slippery and lacks the the ideal handling characteristics of nylon. Its strongest point rests in the fact that it hardly absorbs water and is therefor less likely to ice up while on a climb. Polypropelene has gained popularity as an ideal material for fixed mountain lines on mountaineering ascents, due to its light weight and water repellency.
Nylon is slightly less dense and has better abrasion resistance than does polyester.
It also has better elongation and energy absorption properties than polyester. Neither is prone to mildew and both have comparable melting points and are dimensionally stable over a wide range of temperature. However, nylon loses more strength when wet and sunlight has a greater deterioration effect on nylon when compared to polyester. With respect to the above, nylon is the first choice for the manufacture of climbing ropes. They both have high strength but nylon 66 stretches more under the same load.