At one time, 5.11 offered the same pants (their original model) in either cotton twill or in a stout nylon fabric. I had a pair of each and wore them in the field. One of the cotton types ripped (through the fabric, not along a seam) on their first outing. The other cotton pair got so ratty and faded that my darling spouse (AKA the Domestic Supervisor) threw them out a few weeks ago. The nylon varieties are still in my work wardrobe; the pockets need patching, but they are otherwise unimpaired.

I have a pair of the Duluth Fire hose cotton canvas pants; I like them a lot and they are tough, as advertised, but I would hesitate to wear them in an extreme environment, especially cold and wet; I would shift to synthetics in a heartbeat.