After trying one of these yummy shirts, I have sworn off all polyester t-shirts! Not the itchy wool you might think of, but silky soft, it's cool when it's warm, warm when it's cold, with excellent moisture control. And the big bonus, very low "stink" factor. After a week on Kilimanjaro, these shirts were the only clothes in my duffel that didn't smell bad. Smartwool's usual attention to quality and detail abounds, and once you've tried it, you'll never go back!