The wiggy’s fishnet underwear is absolute junk. Strong words, but it is true. The shirt alone weighs nearly a pound, made of heavy nylon mesh more suitable for making cargo nets than for clothing. Thick nylon like this absorbs water just like cotton. Heavy nylon mesh like this is also damned uncomfortable, IMO.
Quality polyprolene fishnet underwear is made by Brynje.com. I bought the Brynje top from Moosejaw.com long ago, but they no longer sell it. Do a google search for resellers.
Performance-wise, Brynje fishnet is miraculous. It works just as the theory predicts: the holes let the perspiration evaporate on your skin, thereby cooling you when you are overheating (and hence perspiring), but the holes also keep you warm when you are cool, since air is the best insulator. Regardless of how much you perspire, the polyproylene will not absorb much moisture, so evaporative chilling when you stop exercising is not a problem. (Polyprolene absorbs less moisture than any other breathable fabric.)
The big problem I found with the Brynje fishnet is that it begins to stink after a while and then is very hard to get clean again. Precisely because polyproylene won’t absorb water, it also won’t allow wash water to get into the fabric and thereby remove body oils. So the body oils just go rancid. Polyester has a similar problem, to a lesser extent, since polyester will absorb some water.
Nylon absorbs enough water that it is easy to clean. Of course, this absorbtion is why nylon is not a great base layer, performance-wise. I value cleanliness over performance, and so my base layer (and only layer for temperatures above 50F) for many years has been supplex nylon shirt and pants. Silk performs similarly to nylon, while being much more fragile. Can’t relly recommend silk for anything outdoors.
My opinion is that merino wool is overall the best choice for a base layer for use with vapor barrier, unless you don’t care about stinking, in which case polypropylene is best. Wool absorbs huge amounts of water without the fabric structure collapsing. Therefore: (1) wool is very easy to wash, because the water and detergent gets into the fabric and removes the body oils; (2) wool keeps you dry and comfortable until such time as you completely soak the underwear. Provided you have enough intelligence to remove insulation as soon as you begin perspiring (and don’t fall into a lake), this won’t be a problem. Keeping the skin dry is important to prevent funguses and trench foot. (3) wool dries from the inside out (namely, because the structure doesn’t collapse when damp–this is what distinguishes wool from cotton and rayon, and also down for that matter), thus avoiding evaporative chilling problems when you stop exerting yourself.
Merino wool fishnet would be even better than ordinary wool underwear, but no one makes this, as far as I know. The best available alternative is the thinnest possible wool base layer.
Note again that the primary purpose of vapor barrier is NOT to add warmth by preventing evaporative cooling of insensible perspiration (that is a bonus feature that is mainly of interest at extreme temperatures, like -50F), but rather to prevent the insulation from being ruined due to condensation. Provided you have some way of drying out your insulation daily, then vapor barrier is not really needed.