Polymeric fibers are extremely strong along their longitudinal axis. The measure of this strength is commonly referred to as "tensile strength". They have low flexural strength, meaning they are not strong along their horizontal axis, which is why ropes loose significant amounts of strength when tied in knots.

Nylon
The generic name for nylon is "polyamide". Climbing and life safety ropes are made primarily with either nylon 6 or nylon 6,6. Wallace Carothers at the Dupont Institute developed nylon 6,6 in 1935. The high tenacity and relatively low weight made nylon extremely suitable for constructing military parachutes, ropes and cords. Today's nylons are far superior to the early versions. The nylon used in life safety ropes is strong and light with great elongation and impact absorption qualities. Nylon is the superior yarn to use in recreational climbing ropes because of this impact absorption. There is no better product for that purpose at this time.

Polyester
Polyester is another popular fiber used in rope construction. Wallace Carothers first researched polyester during his years with Dupont, but Dupont choose to focus production on nylon. English chemists, John Rex Whinfield and James Tennant Dickson, employees of the Calico Printers Association of Manchester, patented polyester in 1941. Polyester has since made its way into a multitude of products including soda bottles and reflective balloons.
Polyester fibers come in varying qualities. Sterling only uses virgin high quality polyester developed in the last ten years specifically for high strength application in our HTP(tm) Static Ropes and in some accessory cord products.
HTP (High Tenacity Polyester) Static Ropes are a Sterling Innovation. Polyester is a superior fiber to nylon for several reasons. Polyester is hydrophobic, meaning it doesn't absorb water. Polyester has slightly better resistance to ultra violet and is slightly more abrasion resistant. Polyester also has better resistance to many chemicals. The major field applicable difference between polyester and nylon is that polyester has very little stretch. Therefore, ropes made from between polyester and nylon is that polyester has very little stretch. Therefore, ropes made from polyester are not intended for application where there is potential for generating high impact forces. However, this low elongation makes polyester extraordinarily efficient for uses with raises, lowers, rappelling, jugging, highlines and mechanical advantage systems.

Polypropylene
This low strength olefin fiber has s specific gravity less than one allowing it to float. For this reason, polypropylene is used as the sheath in all of our Waterline(tm) Series Ropes protecting and floating our nylon or Spectra core. In certain application, polypropylene is very durable. However, it has a low resistance to heat, UV and many chemicals. There are many different grade and filament levels of polypropylene. Ski tow ropes and generic (hardware store) utility rope often use a low quality monofilament fiber. All our Waterline(tm) products use a high quality, high filament count fiber suitable for life safety use.

Aramids
Aramids are a polyamide as well. The difference is in their molecular structure. The molecules in aramids align into more crystalline formations. The result is a very straight fiber with incredible strength and low elongation. Trade names for aramids are Twaron(r) Technora(r) and Kevlar(r). We use Twaron in our RIT(tm) Series ropes because of its high abrasion resistance and its ability to withstand heat up to 900F. We braid Technora into a supple core for use in our 6mm PowerCord(tm) High Tenacity Cordelette Cord.

Ultra High Molecular Weight Polyethylene
Spectra(r) is an Ultra High Molecular Weight Polyethylene Fiber that has extraordinarily high tensile strength and relatively low stretch. Pound for pound, Spectra is stronger than steel. It has a specific gravity of less than one making it float. We use Spectra in our Spec1000 Waterline and in our 24" and 48" sewn runners because of this high tenacity and light weight. Spectra has a relatively low melting point of between 220-255F and a high lubricity (i.e. it is very slippery) often causing knots to slip.

Until next time, be safe and always dress your knots!