Everything You Need To Know About Rope And Cord Stretching

The topic of stretch comes up almost as much with rope/cordage products as it does with bungee/stretch cord.

As our support desk responds to your phone calls and emails on the topic of stretch, we thought it best to put some notes together that may help you make a decision.

Some Key Points on stretch:

  • Polyester has less stretch than does nylon or polypropylene.
  • Cotton has less than polyester but doesn’t last very long outside.
  • Kevlar and Twaron aramid products have the least amount of stretch known.
  • Our stretch cords (bungee) have about 100% stretch.

Rope And Cord Stretching

Easy stuff first…

Our wide ranging  stretch cord offering (all made in USA by the way) provides products with approximately 100% stretch capability. Stretch cords are subject to heat/cold, over use etc. so that 100% may vary but it’s at least a good initial barometer. Stretch cords have no established reliable break strengths as there are too many variables involved. As with most of our products, we are happy to send out a small sample of just about anything we offer so you can check it out. Just drop us a detailed note of your application or give us a call.

Least stretch to most stretch among cordage and rope products.

Kevlar, Twaron or “aramid” (aramid is the generic name for brands such as Kevlar, Twaron and others) based product will provide you with a very low occurrence of stretch. These super fibers are usually located in the core of the product and protected by a jacket or sheath of polyester or other man made industrial grade fibers. Qualitynylonrope.com offers several  Kevlar and Vectran based cords for low stretch apps such as:

  • Tent guylines where you don’t want the rain or the night’s moisture or even wind to cause a sag.
  • Holding a tarp when you can’t have it slipping at all or the wind beating it to death.
  • Long flagpole application so when you pull a few feet, a few feet and no less moves throughout the entire length.
  • wire core product with UV stable polyester jacket is excellent for flagpole operation and is tamper proof due to the wire inside.
Cotton fiber constructions

While not known for UV stability or abrasion resistance as are the industrial grade fibers we work with, our  cotton is reinforced and stretches fairly low with about 5-10% stretch at break point. Not a bad “one season solution” to a low demand outdoor application.

Polyester fiber constructions

Poor old polyester, still often confused with disco apparel from the 1980’s! The reality is most all industrial /commercial grade cords and ropes for the past 15 years or so are polyester….not nylon.  Polyester has come a very long way and has far exceeded nylon in application range and durability. Polyester (12-15% stretch at break) has about ½ the stretch of nylon making it very popular in outdoor applications where sagging can be an issue. Applications include guylines for military and civilian antennas, tents and fabric structures, awnings, farmers poultry curtains and basic flagpole halyards, UV stabilized industrial grade polyester offers the superior overall performance and price.

Nylon fiber constructions

 Nylon stretches the most… between 15%-30% of its length at break point . Most folks employing ropes or cord rarely push them to their breaking points, but you can expect nylon to provide the give that others won’t. You might want this give when setting up a boat anchor or even a dock line where a bit of elasticity can be a good thing. If you really do need nylon, make sure it’s from us or at least a very reputable store as most nylon that’s labeled as nylon is really polyester or polypropylene. ( see our Dec 2015 Blog for more polyester vs nylon

Polypropylene fibers constructions

Of the industrial man-made fibers polypro is typically the least expensive, stretches a lot (18-22% at break) and isn’t as durable as the others. Polypro can be the soft variety which is called multifilament (MFP) or the hard, monofilament variety (appearance like your weed whacker trim line). Both stretch like nylon does at break point BUT polypro has a tendency to creep (stretch) along the way when under moderate tension which could cause problems depending upon you application. Polypro floats on water and is often seen being used with water skiing, or as a single season tie-down solution. We offer a  twisted polypropylene which is round and  hollow braid polypropylene which is flat, as well as a few solid braid styles.

Stretch cord (bungee) jacket fibers

When it comes to stretch factors, the jacket material used to hold and protect the individual latex rubber ends inside the construction, have typically little to do with how much the product stretches. The jacket performs more for abrasion resistance, UV protection etc, where polyester shines. We offer both a polyester bungee and a polypropylene bungee so you have the choice between performance and economy.

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