Once you start riding in this garment you'll wonder how you ever lived without it. The whole 'insulates when cold' and 'cools you when it's hot' thing sounds like a line cooked up by a marketing department, but it's true. Thermoregulation is what's going on and it works because the merino wool fibers have superior moisture wicking ability, insulating properties, and breathability. In other words, real technical performance that matters...but honestly, we love this base layer because it's comfortable as hell, it outperforms almost any other baselayer out there, it looks really good under your kit, and is incredibly slimming and flattering. It's about as much bang for your buck as you can possibly get! We use ultra-fine merino from the world's premier supplier and believe in it 100%. Fit: Baselayers are meant to be work next to skin, and perform best this way. Ours are slim and true to size.