Light and comfortable. Nice quality.
I only wear short sleeve base layers for cooler or cold temps. I bought this one for cooler (but not cold) shoulder season temps and high-altitude Colorado summer rides. I wanted it to bridge the gap between a lighter-weight LG one (the wind at high altitudes cuts through it too easily) and the slightly heavier-weight Giordana Dri-Release one (which is a bit warm during hard high-altitude climbs in the sun). I wore it yesterday while riding up Pikes Peak (a top 20 world climbing brute) and it perfectly met my goals. It provided the right amount of insulation in the early-morning 50's/60's temps., regulated my body temp & shedded moisture well on the steepest climbing sections, and provided a good buffer against the winds at the top. Thermal comfort was never a thought until I confronted the mid-day 80-90deg temps. back at the bottom (for me this isn't a summer base layer). It's also the most comfortable & best-fitting base layer I've ever owned (snugly close to the body throughout without feeling constraining or distracting, and the material is super-soft feeling). The Dri-Release model is a bit too loose fitting below my chest (great if you put on a winter "roll"), while most others I've owned in sizes that fit similarly close to the body (in this case Assos, Gore, LG and Pearl Izumi) have felt a bit too distractingly like a "sausage casing" and would hinder my breathing. Finally the wide elastic arm & waist bands make them easy to fit under a jersey and bibs without bunching. P.S. Giordana recommends that you size down on this model which wasn't possible for me (I wear a Small to begin with). Instead I think the stretchiness of the material is what allows it to fit close to the body without feeling like a sausage casing. OTOH a smaller size might stretch the material out enough to improve its warm weather performance. I'll never know (and it's not why I bought it), but YMMV!