Synthetic, not cotton. But these things will last forever and feel heavy duty.

https://outlier.nyc/products/experiment-342-bombdeux

The are a few styles in this “Bombtwill” fabric and they’ve held up great for me. I’d only stay away if you work around fire/sparks/etc. They also feel cold when the temperature drops versus cotton. So a wool base layer…not required but do it.

I’d also check out 1620 if you want something more normal. It’s mostly cotton with a blend of high tenacity nylon. You can get yourself double knees, gussets, the whole package. And fire/sparks are not an issue.