North Face ThermoBall™ Traction Mules in Beetroot/Alpine Plum. Your feet work hard, so they deserve the warmth and comfort of the Women’s ThermoBall™ Traction Mules V. These shoes combine ThermoBall™ insulation with high-traction rubber outsoles to make slip-ons that are ideal for base camp, après ski, or shuffling out to grab the morning paper.