Cardio in the cold Layer up with the Smartwool Intraknit Active Long-Sleeve Baselayer Top. Whether we're running through a frosted wonderland or hoofing it up the skin track before finding fresh lines, the techy combination of merino wool and Tencel keeps us comfortable, insulating in the cold and cooling during our workout. Mesh Intraknit ventilation ups breathability for greater comfort, and chafe-free design lets us move to our hearts' content.