Smartwool Men's NTS Mid 250 Bottom. Made from Smartwool's warmest baselayer fabric, the Men's Midweight Bottom is the perfect foundation to your coldest weather wardrobe. The covered elastic waistband and traditional fly design has a natural rise and a heat transfer logo at left hip. Interlock knit with UPF 50 sun protection. Flatlock seam construction eliminates chafing. The Men's Midweight Bottom is warm, yet still breathable for stop and go activities, just what the avid skier or rider needs in a baselayer.