ColdPruf Men's Fire Retardant Single Layer Long Sleeve Crew Neck Base Layer Top 55% Modacrylic, 45% Cotton, Waffle Knit Imported Ring Spun Yarns Provides Exceptional Softness Tag less and Non-binding rib cuffs for comfort True sizing for accurate fit Extended tail for superior neat, secure fit THERMACHOICE SYSTEM: Cold to Very Cold Weather Conditions/Medium to High Activity Levels Ring Spun Yarns Provides Exceptional Softness