Smartwool has always made great products in my eyes and this one keeps the tradition. Worn under a jersey or windbreaker it keeps me warm down to almost freezing. Layering with a heavy jersey or jacket and I'm good down to the low 20's. It regulates temperature very well up to about 55 degrees, then starts getting too warm. It fits close but not restricting at all, very comfortable. Freedom of movement is very good and it doesn't ride up in the back or sleeves. I've washed it several times in the machine in cold water and it's just like new. I highly recommend this baselayer.
The sleeves are long enough! I'm 6'4" with a 37" sleeve and I struggle to find layers that fit well. This is a great base and works well under a jersey and vest in the mid 40s to around 55F. Above that and I peel off the vest. If the temp climbs above the mid 60s, I end up a little warm, but I'm usually wrapping up the ride by that point.
Great design and execution for this base layer, comfortable and warm - perfect for temps in the 50s with a good jersey. For the colder months I would rather use 250 weight fabric but I've layered with this one on 35 degree days and stayed warm enough.
I wore this under a long sleeve during cold weather. I was a great base layer and I would not hesitate to get another if I needed one. My cycling buddy always raves about wool and now I know why!