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Whether you're hiking in cold weather, skiing, snowshoeing, or mountaineering, the REI Heavyweight Polartec(R) Power Dry(R) long underwear bottoms offer excellent value and warm comfort. Polartec Power Dry uses two different yarns on either side of the fabric to enhance comfort, interior yarn wicks moisture and exterior yarn dries quickly. Combination of the two yarns helps keep you dry during highly aerobic activities by moving moisture away from your skin and drying more quickly single-component fabrics. Smooth surface of the outer fabric makes it easy to slide on additional layers. Flatseam construction is soft and non-chafing next to skin; brushed elastic waistband helps ensure a comfortable fit. Fabric offers a UPF rating of 50+ to help protect against harmful UV light. REI Heavyweight Polartec Power Dry long underwear bottoms feature a next-to-skin fit that hugs the body and moves with you. Closeout.