A simple and original favorite, the Men's BodyFit260 Altitude Crewe is a mid-weight layer that leads the pack in high quality New Zealand merino wool natural fiber. Not the wool of the past, the fine fiber and itchless merino wool insulates when wet, is odor-free (unlike synthetics), is incredibly breathable, and offers excellent warmth at half the bulk. This top is perfect as a winter base layer when in the backcountry or by itself during a cool weather aerobic activity. The top features pushed forward side seams with underarm and sleeve inserts for super long wearing comfort and mobility. Arguably, the warmest and most breathable performance base layer available, the Altitude Crewe is designed for cold conditions in a slim, close-to-body performance fit.