I have another Arcteryx mesh cap that I like very much so I picked up 2 of these Poco caps hoping for similar results. It was not to be.
These are simply fitted caps with no adjustments or inner hat band. The material just sits right against your head. If they fit perfectly out of the box, you may do fine. If not, you don't have any recourse. I ordered 2 in the same size, but while one fit pretty well, the other was too loose. While strolling around the smaller fitting one was fine, but when you start to really work and sweat into the hat the material relaxes and gets looser. It ends up feeling like a soggy thing oozing down your head. An elastic band inside would have helped, or at least some sort of adjustment on the back would let you take up the slack as the material wets out.
The brim is sort of rubbery and tends to deform and even get pressed against your face when you are out in a stiff breeze. It regains it's shape well after being stuffed in a pocket which is nice, but it is a bit too soft for breezy alpine use. If you wear it under a hood, the hood also tends to deform the brim and make the view of the world vignetted.
The hat is soft and wicks well, but the fit and overly soft brim limits my enthusiasm for it.