Floso Mens Thermal Underwear Long Sleeve Vest Top (Viscose Premium Range) Viscose, Polyester, 1 x Thermal Long Sleeve Vest. Warm but light weight thermal underwear which will stretch and mold around your body offering maximum comfort and warmth. Viscose material has excellent thermal properties keeping you warm for longer. High wicking rate which is the rate the material carries moisture away from the skin. Fully brushed inside and side seam free for added comfort.