Really like this shirt, perfect for spring runs. Especially like the thumbholes that eliminate gaps between sleeves and gloves. However, should mention that for my long arms, when using the thumbholes, the sleeves are stretched pretty hard. Overall though a really good running shirt.

I may be biased because I hate anything that touches my neck, but the 1/4 zip zipper is almost worse than the benefit you get out of wearing this shirt. As a base-layer it does a great job of both keeping you cool (trhough being dry) and warm. The inner fleecing is soft and the outer covering is smooth enough to let it slide under other garments.

Te thumb loops are great for keeping the snow and cold out. With my long arms, they also kept the sleeves where they should be rather than up by my elbows.

It's hard to say how much energy and fatigue it saves, but I can say that it helps. I almost always have more energy at the end of a day when wearing it than when I wear something else.

I used the the Insulator top for snowshoeing, cross-country/backcountry skiing, alpine skiing, running, cycling worn underneath a jersey. I found that the fabric around the neck kept folding in funny against my neck and creating discomfort and the zipper kept poking me in the neck and chin. The material itself is a great base layer and wicks well so long as you have a breathable layer over it. I would not recommend wearing this shirt without something over it in cool weather. It's super-breathable and almost draws the cold air to you. But, because of that it breathes and works super-well. All in all I think it's a great design if they would just re-work the zipper. If you're used to having a zipper I think you would be fine and it you have a bigger neck I think you would be fine, but since I'm a bit more lean through the neck, the zipper and fabric just weren't working.