This jaunt was thinner than I expected though its doen a good job keeping me warm. The first time I wore it, I was mountain biking at around 30 degrees with only a softshell jacket on top. Frankly, I got cold. I do not believe this is because of the softwool top though, I think its because my softshell jacket is bumsauce. Subsequently, I went for a hike with my dog on a 25 degree morning. On this hike I was really able to feel the temperature regulating properties the shirt claims to have. This time, I wore the softwool under a long sleeve cotton shirt and a light down synthetic jacket. The trails on which I was hiking vary in terms of intensity. During high intensity portions of the hike when I felt my brow start to sweat, the smartwool shirt felt like coolmax material to me and I noticed wicking taking place and that I wasn't getting cold. During less intense portions of the hike, or when the wind blew, the shirt made me feel warm. I'm not trying to suggest that this shirt changes temperature like those hypercolor shirts used to change colors. All I'm saying is that it was nice to have something that regulates temperature as a base layer, so that over it you don't need to layer excessively. For this purpose, and not necessarily to stay warm in very cold temperatures, this shirt excels.

Now for the important part: I'm 6 foot 190. I buy my dress shirts w/ a 33 sleeve. For the smartwool shirt I bought an L. It fits a bit long in the arms - not bad, and it definitely fits long in waist/length area. Overall its just a tad baggy. I probably should've ordered the M - though it would've fit pretty tight, I kind of like that in my basest layer. Its not so bad I need to return though.

I'm a big fan of merino wool, in fact I'm progressively phasing out my synthetic base and mid layers. So yeah, with merino you always get superb breathability, wicking, quick drying and insulation while wet. It's also a lot softer than wool. However this North Face merino crew is unbelievably soft. Seriously, I had to check the label a few times to make sure it was 100% merino wool. I own, use and love other merino wool shirts, and love them, but they're not as soft as this guy.
*Please note this is the same review that I posted for TNF Softwool Crew. I bought both at the same time.