Related to this - all fabrics used by the military need to be both Berry-amendment compliant, and NIR compliant. What that means is that, first, they need to be made in the USA (because you don't want to outsource military equipment if you end up going to war with the country that makes shit for you), and second, it needs to not show up like a sore thumb under infrared light, A lot of fabrics and dyes will show up as hot spots under IR, which means that they show up great with night vision. NIR-compliant fabrics will still appear camouflaged under IR.

That's why those nylon-cotton blend Crytek combat pants are something like $450, when the Chinese knock-offs made in poly-cotton are about $70.