The polyester draws sweat away from the body during activity and allows it to evaporate. It is durable and quick drying, allowing you to go from adventure to adventure. Designed with raglan sleeves allowing for increased range of motion without restriction, integrated thumb loops on the cuff to help with warmth and coverage.  Polyester is also a great hypoallergenic baselayer choice for those who may be irritated by wool or cotton. The added Spandex gives ease of movement and flatlocked seams reduce chafing.