Thermo-X layering fabrics provide incredible insulation with low bulk and quick-dry properties. 50+ U.P.F. Maximum Protection Base-Layer Insulation Quick Dry 4-Way Stretch Fabric Strategic Seam Placement Rash Protection Super Low Neck: No Interference with Wetsuit Neck Boardshort Connector Cinch Cord Performance Fit: Form-Fitting Tight Layer Fits Like A Second Skin Thermo-X HyperDry: 210gsm Nylon/Spandex with HyperDry Technology For Maximum Insulation and Minimal Water Absorption Flatlock Stitched: Breathable Seams | O'Neill Men's Thermo-X Short Sleeves Crew in Black, Size Small, Nylon/Spandex