Thinner and softer than my Icebreaker 150, which I also love. I like the collar on these Stoics though..better for a base layer..the Icebreaker neck is a bit too big. Just depends on your preference. Definitely a softer feel to these Stoics, but I'm afraid a little more fragile. I snagged it a bit and got a rip in one of my sleeves way too easily. Overall, thumbs up..I wear these shirts solo for cooler weather activity or spring temps about town, and am plenty warm. I have several heavier weight merinos (Icebreak et al.) and I love 'em, but I am starting to prefer these lighter weights (150 and 200). Granted, I run a little warm, but even in our coolish Montana weather, these lighter merinos are fine on their own for strenuous activities in all but the stormiest weather. Add a shell or insulated out layer and can go hard all winter. I put a 260 Icebreaker over one of these tops and am usually crazy warm in freezing temps. 5'11" 185 and have the Large, and is just right for me..form fitting but not a spectacle when worn alone in public. Mediums would better for thinner builds or without a slight beer repository to cover up. As other have noted, sleeves run crazy long, but is not a real bother due to adequate tightness in the wrist cuff. By contrast, Icebreaker have more normal, i.e. correct, sleeve lengths, but are also looser in the forearm. In a nutshell, I love these tops when they're on sale, worth every penny. However, it's a harder sell for me at full price over Icebreaker..as price gets about the same, I'd lean toward IB.