Cotton kills, and nowhere is this truer than in climbing, with its sweaty sprints followed by cold belays and frequent rests. The PATAGONIA WOOL 1 ($75, patagonia.com) is the new answer, with a 63 percent merino wool and 37 percent all-recycled polyester blend for warmth and wicking in a lightweight (3.1oz) T-shirt. The Wool 1 kept me warm and unstanky on a late-spring approach into the Flatirons — yes! Then on the rock, the crew collar provided max comfort, and the offset seams enhanced mobility — no binding/chafi ng when reaching. Colors are Desert Clay, Feather Grey, Jacaranda Green, Pirate Blue, and Wildwood; sizes XS to XL.