Page 71 - Bob Holtzman "The Field Guide to Knots How to Identify.."

Polypropylene

Among the least expensive and weakest of synthetic cordage fibers,
polypropylene (also known as polypro or simply “poly”) is very light in weight,
floating higher in water than polyethylene. It does not shrink when wet, but it is
less durable than polyethylene and it degrades quickly with exposure to sunlight,
making it inappropriate for long-term outdoor structures or tying up boats. It
melts at such a low temperature that it can be damaged just sitting in a closed car
on a hot day. The fiber comes in several forms, each lending different
characteristics to rope. Polypropylene monofilaments offer the best wear
resistance; multifilaments are softer and hold knots better; staple-spun and
fibrillated fibers provide a soft, hairy feel; and split-film fibers are the least
expensive.

Polyethylene

Polyethylene rope floats and has good abrasion resistance, making it attractive as
a tow line for water skiing, wakeboarding, and similar sports. It is slipperier than
polypropylene, does not hold knots well, and melts at a fairly low temperature.

Polyester

®
Often sold under the trade name Dacron , polyester is almost as strong as nylon
when dry, and stronger when wet. It has good durability and knot-holding
ability. Polyester rope has moderate stretch, and some types can be purchased
pre-stretched for lower elongation in use. It does not float.

High-tech Fibers
Two more synthetic rope materials bear mention, if only to warn against

spending a lot of money on high-tech rope with limited practical applications for
outdoor activities. Both aramid (Kevlar is the best-known brand name) and
®
high-modulus polyethylene (HMPE or HMP, best known as the brands Spectra ®
and Dyneema ) fibers are extremely strong—some three times stronger than
®
nylon—and both exhibit minimal stretch, but neither can be readily knotted
without greatly reducing their strength, so splices and special termination fittings
are commonly used. Absent some very compelling reason (HMPE is used in
combination with other fibers in some specialized static climbing ropes), these
exotic and expensive fibers are best left to high-end sailboat racers.

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