Expedition Weight Long Underwear Crew Top, Polypropylene & Lycra Baselayering Pol BodyExpanse System features a Lycra strip to expand & provide 4-way flex during movement. ThumbClench System features a Lycra strap that slides on the thumb to prevent bunching when adding outerlayers. Reinforced Elbows for added durability. Tagless Label & Flat Seams for added comfort. Zip Pocket for storage.