Innovative blend of fibers produces a unique fabric that generates a thermal effect. The fabric is technically superior than other fabrics of the same weight, therefore performing much better in keeping you warm. The combination of acrylic and specially engineered viloft viscose fiber provides excellent warmth retention. This stretch base layer fabric provides ultimate flexibility, comfort and moisture-management. Fly opening. Stanfield’s® Heatfx® logo waistband. Anatomical fit.