Wednesday, July 2, 2014

Fabric Strength and Durability – Reality vs. Perception

In this post I just wanted to share a few thoughts with you that were prompted by some questions I got from readers. In particular, people seem concerned about the strength and durability of backpacks and clothing. We hear a lot online about how people bushwhack a lot so they need such and such material for their pack or clothing so that it can stand up to the use.

That is certainly a good idea, but what I’ve noticed is that people often make their choices based on feel and perception rather than actual research. More specifically, we often confuse the thickness of a material, or how robust it feels to us when we hold it, with the material’s actual strength.


You have probably seen that a lot when it comes to tarps, backpacks and outer clothing. Very often people try to explain how they are using a canvas pack or a canvas jacket because it is much stronger and more durable than the nylon (synthetic) counterpart, or how they carry a waxed canvas tarp because it will last them forever. This assertion with respect to a specific jacket or pack may or may not be true depending on the thicknesses of the two materials being compared. An extremely thick canvas jacket may very well be stronger than a very thin nylon jacket, but that does not tell us much about the strength of the materials themselves.

The reality is that, just to continue with the above example, nylon is quite a bit stronger than cotton canvas. The tenacity (load per linear density) of cotton canvas is 3.0 to 4.9 grams/denier. Type 66 nylon on the other hand, which is commonly used in backpacks, tarps, etc, has a tenacity of 6.0 to 9.5 grams/denier. As a rough rule of thumb, nylon is about twice as strong as cotton canvas for the same density of material. That would mean that a nylon tarp can be half the thickness of a canvas tarp, and still be just as strong. Of course, if you take cotton canvas that is three times as thick as its nylon counterpart, it will be stronger as a whole.

When it comes to abrasion resistance, cotton canvas is rated as low, while nylon cordura is rated as good.

Or, maybe you have heard people speak about the durability and strength of their wool clothing. The tenacity of wool is about 1.6 grams/denier, weaker than cotton, and much weaker than nylon derivatives. In fact, wool is notoriously easy to wear out. That is why until recently you would mainly see it as a mix with synthetic threads.

The above differences however can not be detected by our senses, so too often we will just hold a material in our hands, and conclude that the one that is thicker and “feels more solid” is in fact the stronger one. That is not necessarily true. In the above example, if you got two tarps of the same thickness, one made from cotton canvas while the other made from nylon cordura, the nylon one would likely be twice as strong as the cotton one. Alternatively, you can get the two tarps with equal strength, but the nylon one would be half the thickness, with the corresponding weight and volume savings.

A further wrinkle in all this is that sometimes people compare the strength of materials that are not the actual material. Most often you can see that in claims about how GoreTex is not very strong. It is usually in the context of how a person does a lot of bushwhacking and they don’t want a weak GoreTex jacket, so they carry a waxed canvas one. The comparisons are quite absurd, as GoreTex is not the actual fabric at all. It is simply a microscopic membrane. The material that we see as a final product is the GoreTex membrane bonded to some other material. That other material can be anything from extremely thin to extremely robust and durable. How well a GoreTex jacket holds up to use will depend on the type of material to which the membrane is bonded. That material may very well be much stronger than the cotton canvas alternative. 

Anyway, this is just some food for thought. Thicker materials always seem stronger to us, but it’s not necessarily the case. If you are concerned with strength, look at the strength of the individual materials, select the strongest one, and then get it in the desired thickness. Don’t just go by whatever seems the strongest to you. 

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