Ahh, it's a good day when a model piece of minimalist gear comes along. The Patagonia Nano Puff pullover definitely fits the bill, weighing in at a scale-verified nine ounces even (odd?) for a men's medium.
The Nano Puff doesn't have a lot to review in terms of features, and that is by design. There is a single zipped chest pocket that the pullover will stuff into, a nice deep half-zip on the front with a neck-protecting zipper garage at the top, and some elastic around the cuffs and hem. That would be it.
The medium is true to size, by which we mean it actually fits like a medium: trim but not snug, with room to move without feeling like a seam is straining somewhere. As a layering piece it's pretty much perfect. The slick material won't bind under a shell, and the hem rides right at waist level so it will nest nicely with a harness and belay jacket.
The Primaloft One synthetic fill is awesomely warm for the weight, and we like that we can use it inside a down sleeping bag or down parka and it will intercept our nasty moist body skank before it compromises the down fill. The Nano Puff works great on its own too. It's got the usual Patagonia premium pricing, but in this case we're inclined to say its worth it.