Testers Nancy Prichard Bouchard, Berne Broudy, Jonathan Dorn, Kristin Hostetter, Dennis Lewon, Molly Loomis, Kris Wagner

You could live in this Patagonia merino baselayer for weeks.

When it's extra cold, don this full body baselayer by Outdoor Research.

Worn as underwear, or solo, these "runner shorts" are a versatile bottom base layer.

This Icebreaker top is great for trail running and other high aerobic activities.

This First Ascent top works as a baselayer and a jacket.

This athletic baselayer feels like cotton but works like high-priced synthetic, for only $35.