"Doesn't look like much, but looks can be decieving"
When you hold this piece of clothing its super thin and doesn't look to warm. However, its a great layer and wicks away moisture, sweat, etc. Even though its a great layer, its thin, so it can be great to wear on a chillier hiking day...keeps you from being col, but doesn't cause you to overheat.
when you first look at this shirt it is surprising because you can see through it (unlike the capilene 3 shirt) which made me wonder how it could possibly be warmer than that one. i don't claim to understand the construction (some kind of baffling) but it works. super warm base layer. form fitting, 5'10" 140lbs and the small fits perfect.