I bought this shirt for when I am in full sun for sun protection.  It is very thin linen/gauze like material almost see through. It works well.  The day I wore it the weather was about 100 degrees f, with very high humility.  Although I was sweating because I was working digging, the shirt did get drenched in sweat.  But with a breeze it felt cooler.

As for sizing, I am a male average built, may be a tad slender, 5'10", and I bought the XXXL size.  I washed it first in warm water and dried it in the dryer.  It shrunk a full size+ as expected.  The shirt is nice airy and roomy and does not cling on the body as a tighter shirt size may do.

Overall I am very pleased with this shirt and with the larger size I bought.  When in doubt, go with the larger size as you can always wash and dry it in hot as to make it shrink more.