How do you determine the breaking strength of polypropylene webbing? It depends. There is no industry standard way defining breaking strength. One manufacturer might test 10 samples and take the lowest strength. Another might take the average and a third might take the highest. Being a commercial grade product that is not designed for use in life safety or overhead lifting no government agency is telling the manufacturers what to do.
The industry has two basic models of polypropylene webbing, lightweight and heavyweight. American Cord and Webbing (ACW) has their 549 material that ranges from 0.040″ to 0.060″ in thickness and in a 1″ width has a minimum breaking strength of 360 pounds. ACW’s heavyweight material has a thickness range of 0.055″ to 0.075″ and a minimum breaking strength of 560 pounds.
I have seen lightweight 1″ material listed as having a 600 or even 700 pound breaking strength. Is one better or different from the other, probably not.
What makes piece of webbing strong is the amount of material (polypropylene in this case) it contains and how it is constructed. Thickness tells you something about the amount of material for a given width.
So how do you figure out what to use? First the webbing is usually not the weak point in a strap assembly. Stitching or buckles can be much weaker. A 1″ side release buckle will have a breaking strength of around 200 pounds, much lower than ACW’s 360 pound breaking strength for the webbing. If you have a critical application the only way to be sure is to make some assemblies and test them. If all you are doing is strapping up some sleeping bags, strength is not an issue.
With polypropylene webbing chafe and ultra-violet (UV) exposure are two issues which will weaken your strap. Materials like polyester offer much better abrasion and UV resistance along with a higher initial strength. If you are repeatedly loading a strap consider nylon whose ability to stretch might help dampen the load.
My article How Strong Is Your Strap covers sewing pattern choices. Searching the internet you can find other information that will be helpful but at the end of the day, build a prototype and test.
Straps to Go stocks 4 basic types of nylon webbing:
Standard weight with a breaking strength of around 900 pounds for 1″ width material.
Heavy weight with a breaking strength of around 2750 pounds for 1″ width material.
Mil-Spec with a breaking strength of 1200 pounds for 1″ material.
Tubular with a breaking strength of 4000 pounds for 1″ material.
The image above shows commercial grade webbing in both standard weight (on the left in light green) and heavy weight (on the right in dark green). Note that when I listed the breaking strengths above, I said “about” since these are not load rated goods.
Here we have Mil-Spec webbing in Coyote Tan and standard weight nylon webbing in green. You can see the construction is different and the Mil-Spec webbing has a breaking strength of 1200 pounds (this material has a design strength unlike the commercial grade products).
This gives you an idea of the construction difference between the Mil-Spec and commercial nylon webbings.
Tubular construction is the strongest of our nylon webbings. It is really two layers of webbing so you get a breaking strength of 4000 pounds in a 1″ width.
This view gives you a good idea of the amount of nylon used in the tubular construction which is why you get the added strength.
What is each type best suited for:
Standard weight is great for tie downs and general purpose straps. It is used on backpacks for attachment points and it works well with single lock buckles and slides to allow for adjustment.
Heavy weight nylon is used extensively for pet leashes and collars. It feels nice in your hand (this is why it is used for leash’s, not that you need the strength) or around your pets neck. We also sell it for heavy duty tie downs. We stock a wider range of colors in the heavy weight product than our other offerings.
Mil-Spec nylon is used in the same way as the standard weight commercial product. It is a bit stronger but the trade off is in stiffness. If you are making MOLLE loops, this webbing would be a good choice.
Tubular nylon is the climbers friend. Slings and attachment points are commonly made using tubular nylon. It holds a knot well and feels good in the hand.
If you have questions on what product would best meet your needs, give us a call at (253) 883-5800 and ask for Rollie.