Here's what other sites are saying:
The women's REI Lightweight Polartec(R) Power Dry(R) long underwear bottoms are an excellent performance insulating layer for aerobic activities in cold weather. Polartec Power Dry utilizes 2 different yarns on either side of the fabric to enhance comfort: interior yarn wicks moisture, and exterior yarn dries quickly. The combination of the 2 yarns helps keep you dry during highly aerobic activities because it moves moisture away from skin faster than single-component fabrics such as cotton. Updated fabric protects skin against harmful ultraviolet light with a UPF rating of 20 and is very soft to the touch. Flatseam construction is soft and non-chafing next to skin. Brushed elastic waistband ensures a comfortable fit outing after outing. Low-bulkiness fit makes it really easy to layer under a shell or additional insulation. The women's REI Lightweight Polartec Power Dry long underwear bottoms feature a next-to-skin fit that hugs the body and boosts fabric performance.