Don't pay attention to the sizing guidelines AT ALL. I ordered according to my measurements and probably need at least 2 sizes smaller.
I am 5'4" and about 128 lbs. I ordered a medium according to my measurements. Also, because of my height I have a really hard time finding pants that aren't too long or too short. Petite is perfect until I wash them a few times and then they're high waters. Regulars are always a bit too long. These in regular say they measure 31", I measured myself at about 30" so they shouldn't have been too bad but they almost completely covered my feet.

As far as the material goes, it seemed kind of stiff, and possibly like they would be hot in the summer. But then, I never did get to wear them because they were just far too big.