Mesh baselayers having a “craze” feels weird to even say out loud, but I kept hearing the same claims: they’re lighter, warmer, and keep you drier than a normal closed-weave base layer. Some sources even say mesh is four to six times warmer at the same weight—which sounded pretty wild to me. So I did what I always do: I tested it. I grabbed a Brynje-style mesh shirt, ran a controlled home test with my homemade thermal mannequin in a freezer, and then took both a mesh layer and a standard baselayer out for the exact same winter hike in Colorado. In the lab test, the mesh layer used about 20% less energy to hold the same temperature, which means it was roughly 20% warmer than the closed weave shirt I compared it to. That’s nowhere near “four to six times,” but it’s still impressive considering it’s basically a shirt full of holes. On the hike, I weighed each layer before and after to see how much sweat they held. The standard layer retained under an ounce of moisture and you could see it around my stomach and chest, while the mesh baselayer weighed exactly the same at the bottom and the top—meaning it retained no sweat at all. My takeaway: mesh can be warmer and dramatically drier, but it only really shines if you’re using smart layering and venting.