To achieve high thermal insulation without increasing weight, Waterproof's Body X and Body 2X Undergarments are made of a hollow fiber polyester. Inspired by the structure of the fur of a polar bear who lives under extreme environmental conditions. It insulates far better than a regular fiber because it is hollow and filled with air. It's all about keeping warm and dry. The technically advanced fabric in the Body X and Body 2X has excellent moisture-wicking properties. It is designed to pull moisture away from the skin by capillary action and out to the exterior of the fabric where it easily evaporates. The combination of hollow fiber insulation and the excellent wicking properties creates an extremely warm and comfortable undergarment. We are all different. Not just the way we look, we also react differently to warm and cold, activity and rest. Therefore, the undergarments are separated letting you choose different sizes and different insulations for the upper and lower body. Choose any combination you like. Newly developed, highly functional fleece material for an optimal body climate. Power Stretch Hollow Fiber- Better insulation than regular fiber because it is hollow and filled with air. (90% Polyester 10% Elastane). Two-piece fleece underwear with power stretch providing freedom of movement. Highly pill-resistant brushed fabric is next to skin for longevity of the garment and added comfort. (Anti Pilling ASTM D 3512. Grade 4.0). Gender specific, flatlock seams,