I love these shirts! I first bought a couple when searching for new long underwear, (to wear when working outside in the winter.) These worked great, are very soft and comfortable, and long enough to stay tucked into a waistband properly. They also come in a couple different weights, and all keep me plenty warm, while being very breathable and good at wicking away moisture, so they're also not too hot in warmer temperatures. I liked them so much I started wearing them as casual shirts around the house, and finally bought more, now in more colors! Inspired by a photo on the product page, I even tried wearing a buttoned collared shirt underneath one, and this looks great- the Duofold shirt looks like a lightweight sweater over the top and classes up nicely. Amazon/Duofold sells them under several different names, but they all seem to be more or less the same.

Tough review to do on this. I purchased both the shirt and trousers. I am 6'0, 210 lbs. I bought the shirt in a Size L and the pants in a Size XL. Both fit pretty well except that they are both on the short side. The Waist is comfortable, even though they pull down in the back when i slightly bend over. They need a little more room in the crotch. I find that the stitching is too tight from the crotch to the butt. The legs come up too short.
The shirt fits really nice for my build but also have a sleeve issue because they're too short. The material and stitching are TOP NOTCH! These feel awesome. They don't itch or irritate and the material is REALLY soft. Even my wife noticed that. I just hope that they can make the minor adjustments with the lengths and these would be a steal! But with that said, I hope these don't catch on too much because i don't want them to sell so much that they raise the price. I want to keep purchasing these!
Just a note here, i'm not a hefty 210 lbs, if that helps. I realize that the weight with height might throw some people off and it might throw the sizing off for you if you are a hefty 210. Just a heads up on that.

This thermal shirt does a great job of keeping you warm during the colder parts of the year. It's a thicker material which is nice. Not super think, but it's thicker than the normal white undershirt you might find at a normal department store. It also washes and cleans very well.

The only problem I have with it is that I am 6' with a longer torso and arms. I ordered the LARGE size. It still fits, but after washing 1-2 times the arms and torso did shrink up a little. So they are just a tiny bit shorter than I would prefer, but other than that, I use these whenever I go out during the winter.

SIZING:
I was a little worried about what would happen when washing this shirt. It seems like many shirts I buy always shrink in the length too much because I am tall at 6". But this one didn't seem to shrink at all or if it did I did't notice it. So that's really nice that it has worked out that way.

I work year round in CT and many of those days are spent outside. During the winter it can be brutally cold on some of the job sites we work on. It may be 20degs in the city area, but 20 miles north at the top of the hill is a different story. For the last 15 years doing concrete work I've learned to wear layers. Going out and working hard wearing the wrong clothing will make you sweat all day. Having multiple layers that you can add/remove as needed is the way to go.

Personally, I wear these thermals as my base layer, followed by a t-shirt, flannel, sweatshirt, etc. They work extremely well keeping body heat in without letting sweat build up. They're as comfortable as one could hope for and do the job well. Not to mention they look good when worn solo. Every year I order another half dozen, just to make sure I always have enough.

The one bad thing I've noticed over the years with these thermals is that after enough wash cycles they do shrink a good amount. For example, a medium shirt fits well out of the box and for the first few washings before it starts to feel like a small. Larges fit on the bigger size out of the box, but over time will begin to feel like a medium. For me this isn't a huge deal because I mostly use these under other shirts. I would recommend buying one of each size you'd expect to be and see for yourself where you land.

Amazon asked me - How does this product fit? I'm not sure how to answer this question because it fits both somewhat large and somewhat small. The arms fit slightly small as it fits like a compression shirt (tight) on my arms from elbow to hand. The torso part hang just slightly large/ slightly too loose. I like but don't love the shirt. Always looking for the perfect undershirt for the winter time. This will suffice for now, but the search will continue...