You might think the protective chaps worn by loggers work through sheer density, by using a material thick enough to provide protection from a fast-moving chain. But that simply isn't physically possible. So instead, the designers of protective chaps have cleverly harnessed the material's property in such a way that it can physically stop the chain from moving:
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Obviously, like bike helmets the chaps are meant to be replaced after an accident. But if you talk to anyone who's ever had or witnessed a chainsaw accident, you'll quickly surmise that protective chaps are well worth the purchase, and cheaper than replacing a leg.
For those of you designers looking into the protective gear market, the warp-knitted technical material on my (Stihl-branded) chaps is called Engtex, made by the company of the same name.