I first tried the 150 Atlas on my recent winter expedition as a base layer under the Icebreaker GT 220 jacket/shirt. I was a little hesitant to change from polypro on such an important trip, and brought my regular base laters just in case- but after the first few climbs up the mountain I was really impressed and never looked back. I am 6'2 190lbs but used the large size to ensure a snug fit- which not only improves layering but is warmer and helps with muscle support during activity. I was told that merino wool would stretch but the Atlas top held its shape (mostly), even after weeks of constant wear, and then it returned to a snug fit after each hand wash. The wicking ability of this shirt is really amazing. Downside: I felt a little itchy at times, but this is a small price to pay for such major improvements in my base layer performance.

Quality is second to none as you would expect from Icebreaker. Great all-season weight and softness as well. However, make sure you really pay attention to the sizing chart. I am 6'3", a very athletic 200lbs and generally wear an XL in just about everything, except this... the XL is too tight in the chest a little on the short side as well, and yes I know this is a base layer and should be snug.

My advice is to pay close attention to the sizing chart (duh) and order based primarily on chest size and then height.

Update, the XXL is a perfect fit.

We discovered Ice Breaker when we hiked Milford and Routburn in New Zealand. Better designs and better made than Smartwool. Great for all weather except Texas summers. I am now on the Tibetan Plateau 4000 meters+ in November and had these on under my fleece and shell.

This is a fantastic top. I have used it so far as a base layer while snowboarding and XC skiing with a midweight on top of it. Breaths well, keeps you dry and warm. Use it day after day and it just dries and never smells. Should also work great as a single layer for aerobic activities on warm to cool days. I'm 5'11" with an average/athletic build and the medium fits perfect. I would call it an "athletic fit" - snug but not tight.

This is my fourth Icebreaker top I've purchased in the last 6 months and it really is great. I don't think I could ever go back to synthetics. It's a good 'athletic' fit that I use as a base layer to run and cycle in. Just be sure to follow the care instructions as described.

There's not much to say about this, except: it works great as a next-to-skin layer (it "seems" a little warmer than thicker n2s layers from other brands); it doesn't itch; it doesn't stink after (no more than) three days.
I am 6'0" / 195 lbs and got the XL. It is form fitting against my spectacular physique.
Very happy with this top - and very, very happy with every little piece of IceBreaker gear I own.

Product is pretty stellar. First piece of Icebreaker, and it will stay a staple in my wardrobe. Compared to the Bodyfit 200, this is a bit itchy on my skin, but barely noticeable after a short wear. The 200 and up gear has a feel that makes you think it is cotton, plus it is more durable. Low stink factor on all icebreaker wear. I wear the shirts for days on end-(three plus) without much or any stink in my pits. Be careful, (the material tore on me once when I was pulling my shirt down.) When soaking wet, it does have a sheepy smell. Go figure.

I love this top! I'm 6' 2" 180lbs and I have an XL which works fine for me. I wear it around the house, or as the base layer to my snowboarding setup. This was my first piece of Icebreaker gear, and I've since bought socks, bottoms, and looking for anything else I can from them.