Icebreaker GT Run Ace Shirt - Sleeveless - Men's

You can wear this as a base layer for extra core warmth on those really "crisp" days or you can wear it alone on a hot day in the desert. I was more surprised by the latter than the former. I think most people would agree than any additional layers of Marino Wool will make you feel that much warmer, but it's not intuitively obvious that it works on hot days as well. It is not what I would wear in the desert with full Sun, but that’s only because it only comes in darker colors. If this were white or off-white, I would wear it in the hottest environment. That’s because it fill up with sweat in the heat and acts like a cooling blanket. Very nice! So I would limit this to the upper-80’s or mid-90’s on the high end, but it is incredibly comfortable in the 50’s, 60’s, 70’s, and low 80’s. That’s a nice range for a single shirt. Adjust to taste.

This is my first piece of icebreaker clothing and merino wool and it is simply amazing. It has quickly become my favorite shirt to wear to the gym and around town running errands. The merino wool with a touch of lycra is soft and has just a slight cling in the chest to be semi-form fitting. I'm 6'7, 235 with a 46" chest and 34" waist and the xxl fits perfect. I will certainly be buying more merino wool and icebreaker clothing.

This shirt is fantastic. I'm a huge fan of merino's performance, and going sleeveless is great for summer adventures. I've worn it on a couple 90 mile bike rides, a few days hiking, a couple runs, and casually a few times. I've yet to wash it, and after all that it still smells fresh and ready to go.

You don't really notice the performance difference between this and other shirts until you go back. It blows cotton out of the water, and while synthetics may wick, they don't feel anywhere near as good doing it.

The only downside to merino is that it's very fragile for how expensive it is. I've avoided wearing this shirt while doing anything that could damage it. For example, I've helped some friends move, and I would have love to wear this for the performance, but just couldn't risk it. I also would hesitate to wear this to the gym I go to (they have us do all kinds of crazy stuff)... although your average gym for lifting/cardio machines wouldn't pose much of a threat.

One last thing to note- merino in general seems to be designed to hug your body. I wanted a looser fit, so instead of the M or L I'd normally order, I went with XL. For what it's worth I'm 6'1" with a thin build. If you're normally on the fence between two sizes like I am with M/L and want to ensure a loser fit, go XL.