What are these made of: "Fabric: 48% polyester, 34% nylon, 18% spandex or, 61% polyester, 25% nylon, 14% spandex"
As for the rest, I own both merino wool base layers + fleece base layers. I like them both for various reasons.
- FLEECE: When I'm on backcountry expeditions, the fleece wins. Extremely lightweight, breathable, dries quickly and very warm depending on the quality/ thickness/ composition.
- MERINO WOOL: Hands down the cosiest, best feeling on my skin, very warm, and wears like iron. Tends to be slightly heavier weight-wise, however. I'll use it for skiing, day hikes, and just keeping warm at home.
I don't work outdoors for a living, but if I were, I might try two base layers... maybe a technical polyester lightweight fleece on the inside, then merino wool as a mid-layer. In fact I often use this combination anyway. Best of both worlds: max breathability of the polyester base, and excellent arming of the merino mid.