There are a ton of base layers out there, and with all those choices, you might be tempted to just grab one off the shelf. But there are some details worth paying attention to, such as the type of fabric, and the weight, thickness, warmth, and wickability of a particular piece. To narrow things down a bit for you, and to clarify some of your options, we’ve listed some of our favorite base layers that we wear on any given day in the mountains or around town. We’ll be adding to this index going forward, but it should give you a head-start in shopping for a new layer. We’ve split these products up into loose categories based on their material—ranging from pure merino wool, to merino / synthetic blends, to fully synthetic fabrics. We’ve also included an underwear section at the end, with our take on some more athletic underwear options Also note that most of the wool and wool-blend base layers have a fabric weight listed. This should give you a relative sense of how thin or thick those pieces are. (A fabric with a weight of 150 g/m2 is quite thin, while a 250g/m2 piece will be quite a bit thicker and warmer.) Wool TREW Weightless NuYarn Merino T Fabric Weight: 105 g/m2Material: 85% merino wool, 15% nylonMSRP: $65 TREW Weightless NuYarn Merino T NuYarn is an interesting take on a merino/synthetic hybrid, and it certainly stands out among the other wool fabrics when it comes to stretch, comfort, and lightweight feel. The NuYarn fabric is the softest and most comfortable of the wool base layers, and it seemed to wick sweat better and absorb less water than the other wool pieces. The fabric averaged about 2 runs before acquiring much of a smell. Using the lightest version of TREW’s NuYarn fabric, the Weightless NuYarn Merino T is our favorite of the wool base layers here for hot days. As its name suggests, the Weightless NuYarn Merino T feels very light on skin, and it’s easy to forget you’re wearing it. It fits a bit slimmer than what we’d call a “regular” fit, but is looser than the Mons Royale Yamakasi and Smartwool PhD Ultralight shirts. TREW Superlight NuYarn Merino Pocket T Fabric Weight: 125 g/m2Material: 85% merino wool, 15 % nylonMSRP: $69 TREW Superlight NuYarn Merino Pocket T The addition of the stretch-woven pocket makes the Superlight NuYarn Merino Pocket T a great everyday piece, though the performance characteristics of its fabric also make it a strong contender as an all-purpose base layer. Like the Weightless NuYarn Merino T, the Superlight NuYarn Merino Pocket T offers a great blend of breathability, stretch, comfort, and lightweight feel, and also shares a similar, fairly slim fit. Luke Koppa in the TREW Superlight NuYarn Merino Pocket T, St Mary’s Glacier, CO.
