Smartwool balances maximum insulation and technical breathability in the Intraknit Thermal Max Merino 1/4-Zip Baselayer Top. The warmest in Smartwool's Intraknit lineup, this baselayer top is made with body-mapped ingenuity that puts warmth, airflow, and articulation in the zones we need most. This lets us stay active when temperatures are deeply below freezing without worrying about thermoregulation or moisture buildup. Of course, the techy merino wool fibers always help with that, all while being naturally odor-resistant and oh-so-soft.