Nylon is the strongest easily available rope material. Although it is quite strong it does lose about 15% of its strength when wet. In most cases, this is not significant, but it should be factored into the rope-buying decision for applications where the rope will be exposed to water. It should also be noted that it is very dense and sinks in water.
Nylon is the best choice of rope for many applications. This includes marine, general purpose, and towing. It is very strong, but perhaps more importantly highly UV and abrasion resistant, so it lasts a long time. The most commonly available nylon ropes are white and may be marketed as “dock lines” or “anchor lines”. Nylon ropes excel at both of these tasks.
Polypropylene rope is most popular due to it’s price. Of the synthetic fibers it is the cheapest. It is strong for it’s weight, but it is not very UV, heat, or abrasion resistant. For this reason, it is generally not a good choice for long term applications where the rope would be exposed to sun or abrasion (e.g. a dock line). Polypropylene’s only redeeming characteristic other than it’s excellent price is that it floats. In some applications (e.g. rescue line) this is an important feature.
Polypropylene is the best choice for budget conscious applications where the rope will not be exposed to abrasion or UV for extended periods of time or where buoyancy is needed. This includes cheap disposable twine, general purpose budget ropes, and infrequently used ropes. This rope is commonly available in yellow as “value packs” or as cheap twine sold in hardware stores.
Polyester is almost as strong as nylon, but it does not lose strength when wet. It also has the highest resistance to abrasion, UV, and heat. The main difference between nylon and polyester is the elasticity – nylon stretches significantly more than polyester. Polyester is also more expensive and not as easy to work with . It is also more difficult to untie than nylon.
Because of these factors, nylon is more appropriate for applications where slight stretch is desirable, such as dock lines or the core of dynamic climbing ropes. Similarly, polyester line is more appropriate for applications where stretch is not desired, such as lifting slings and hammock guy lines.