It uses a unique two-layer construction where the outer layer is 100 percent merino wool and the interior is synthetic.

Helly Hansen Lifa Merino Seamless Top for $110 ( Women's, Men's ($77) ): Senior associate editor Adrienne So says it's incredibly stretchy and light, and thin enough to fit under the snuggest mid-layer.

But for a casual day hike or car-camping trip, these sticking points don't matter as much. Uniqlo Heattech Crew Neck Long Sleeve T-Shirt for $20 ( Women's, Men's ): This long-sleeve base layer blend of polyester, acrylic, rayon, and spandex isn't technically an outdoor garment, as the seams are in the wrong places for an outdoor base layer and there are no bonus features, such as thumb-loops.But the fit of the Woolies is great, the flat seams sit away from parts of the shoulders that rub on backpack straps, and the fabric is pillowy soft. Ibex Woolies Tech Long Sleeve Crewe for $115 ( Women's, Men's ): This 81-percent merino/19-percent synthetic base layer would be a contender for best merino base layer, except the Smartwool is cheaper.The fabric hangs perfectly without clinging or riding up, and it dries within a few hours. It is senior associate editor Adrienne So's go-to for outdoor runs. Tracksmith Harrier Long Sleeve Top for $84 ( Women's, Men's ): Another blend of merino wool and synthetic, the Harrier is a basic base layer without fancy details or offset stitching.The following are a few others we like, though not enough to give them a slot above: We've tested more than a dozen base layers. Size up: When I tried one on in my usual size, I looked like Randy Quaid with his belly bursting out of his sweater in Christmas Vacation. I prefer a separate buff, but it's a nice feature. When it's down, it fits tightly around your neck to trap warmth. When the hood is up, you can bring the lower part over your mouth. That can be a positive or a negative, depending on whether your body runs hot or cool. The Air Hoody is true to its name: very light yet warmer than other lightweight base layers. That means no chafing when you're carrying a pack. It's also nearly impossible to feel the seams. It's surprisingly good at blocking air for a base layer.

All base layers stretch to some extent, but the Air Hoody is particularly stretchy and form-fitting.īecause the material is knit, I expected wind to cut through it, but I was wrong. It's a blend of 51 percent merino wool and 49 percent recycled polyester. Subscriptions help fund the work we do every day.Īfter a brief absence, Patagonia's Capilene Air Hoody is back, and it remains a favorite. This includes unlimited access to and our print magazine (if you'd like). Special offer for Gear readers: Get a 1-year subscription to WIRED for $5 ($25 off). We've added the Patagonia Capilene Cool Daily, Smartwool Short Sleeve, and Smartwool Merino Short Sleeve, and we've updated pricing and availability throughout. Updated April 2022: We've added short-sleeve base layer picks for your warm-weather adventures. There are a lot of undershirts and base layers few are terrible, but few really stand out. Even on comfortable 70-degree days, you can get hypothermia if you stay wet for too long in a breeze or over the course of a chilly night.

It has to be comfortable and non-chafing, and it needs to wick away sweat to the outer clothing layers so you won't stay damp. From the choice in fabrics to the location of the seams, a lot of engineering goes into an outdoor base layer that sets it apart from a common cotton undershirt. The base layer (outdoor industry-speak for 'undergarment') is the foundation for your entire outdoor clothing system, and it all starts next to the skin. You might think a snug-fitting top is a garment only for chilly days, but it can be a vital piece of gear for sunny-day treks too.

Now that we've exited what was seemingly the longest winter ever and entered spring, our thoughts turn to all the warm-weather adventures we're going to have across national and state parks, campsites, climbing walls, and day trails.

Merino mix base layer