have been supremely pleased with the short and long sleeve merino wool rapha undershirts. ride 5-6k miles a year and wear at least one regardless of how hot or cold it is on every ride. i get about 2.5-3 years worth of use out of each one. granted, at this point, i've got 6 of their underlayers. no matter how soaked it gets from rain or sweat, they keep you warm. a true miracle material. not inexpensive at $85 (for the short sleeve-nonsale pricing) a pop but the best piece of clothing i own. period.