REI Airflyte Top
Here's what other sites are saying:
With moisture-wicking, quick drying technical fabric, the heavyweight REI Airflyte long underwear top keeps kids warm and comfortable in cold weather. The low mock neck is warm but not restrictive. Stretchy polyester/spandex fabric provides freedom of movement and formfitting style. Thumbholes in the cuffs keep the tops of hands warm and help keep sleeves in place. Fabric provides UPF 50+ sun protection, shielding skin from harmful ultraviolet rays.