Don't buy this shirt if you hate clothing that feels incredible, that breathes well, that has four-way stretch yet retains it's shape, and that works as well as a baselayer on the slopes as it does as a baselayer on the couch. Don't buy this if you like any of the other shirts you have in your closet, because they'll ultimately all wind up with hurt feelings after you stop wearing them and wear this shirt for 6-7 days in a row. Speaking of which, don't buy this shirt if you have friends who will judge you for wearing the same shirt for 6-7 days in a row, because, like I said, that's a risk you're taking by picking up one of these. Maybe, most importantly, don't buy this shirt because I'm a size medium, and Trew seems to be low on inventory in my size, and I'd like to pick up about 6 more of these in different colors.
In all seriousness, this is the only t-shirt I want to wear anymore. Best blend of merino I've experienced; cut really well; stretches and retains its shape incredibly well. I've used baselayers from Smartwool, Patagonia, North Face, and Lululemon, and after getting one of these shirts, I don't want to wear anything else. Can't say enough good things about the NuYarn material and the design of these tees by the Trew team.