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Types of Strength
There are many different kinds of rope because there are many different ways in which a rope can be made strong. The strength of a rope depends on four factors. First is its basic strength, measured in terms of how heavy a load the rope can lift without breaking. Second is abrasion resistance, which determines how long a rope will last without wearing out or weakening. Third, water repellency keeps the rope from swelling or becoming stiff when wet. Finally, the rope's flexibility determines how well the rope can twist and bend while retaining its strength. The overall strength of a rope is determined by these four different factors, and the right rope for the job is determined by which types of strength are most important.
Manila Hemp
Rope has been made from a variety of natural materials, but the strongest natural material available for rope is manila hemp. Manila hemp comes from the trunk of the abaca tree, a relative of the banana that is native to the Philippines. Manila ropes display great abrasion resistance and for centuries were the strongest ropes available.
Nylon
Manila ropes lost their preeminance when nylon ropes appeared. Nylon ropes are extremely elastic, and they are twice as strong as Manila ropes. Today, nylon is an extremely popular material for sailing and climbing ropes.
Polyester and Polypropylene
Nylon ropes have one major weaknesses: They lose elasticity and strength when wet. Polyester and polypropylene ropes are less elastic than nylon ropes, but both retain their strength when wet and are highly resistant to chemicals. Polypropylene rope can float indefinitely, though it degrades in UV light. These materials are often blended to make composite ropes that are stronger than either material on its own.
Specialty Materials
Steel ropes are the ultimate in pure strength; they can lift extremely heavy loads. Steel rope measures low on abrasion resistance and loses strength when kinked. Steel's weight and stiffness make it unsuited to many day-to-day applications.
Even stronger than steel is Dyneema, a synthetic fiber billed as "The World's Strongest Fiber." Dyneema is 15 times stronger than steel on a weight-for-weight basis, and it's light enough to float in water. Dyneema ropes are expensive but have gained popularity among yachtsmen and in industry.