If you're using them to try to keep warm, I'd use heavy weight merino base layers or even polar weight poly base layers if you're sitting all day. But for active all day moving, warm weather, mountain hunting, I haven't found anything better than lightweight merino base layers. But I prefer First Lite to KUIU.hey guys, wondering if anyone's been using their Kuiu nuyarn basel layers? What're your thoughts? I wore mine under my North Branch bibs and it high twenties/low thirties my legs were cold... should I have doubled up on the base layers or what?