The toughest pants I've ever had are the military issue 50/50 cotton/nylon BDU pants, temperate climate weight. The "summer weight" ones are thinner. They're slightly heavy for hiking and such, but not bad, particularly if a lighter weight shirt is worn. Wearing both the upper and lower BDU uniform on a hot day wasn't much fun. The are 50% cotton, so they don't dry all that quickly, but they're good as work pants and the like.

I'm with AKSAR, though, for the outdoors I like 100% nylon. Light, tough, dries quickly.

HJ