The Best Backpacking Baselayers of 2021
The best backpacking baselayers wick sweat and regulate temperature for superior next-to-skin comfort. This is one gear category you don’t need to overthink—although they vary from one garment to the next, baselayers are pretty straightforward overall. Still, we’ll talk you through the best materials and other features to look for in the best backpacking baselayers.
Best Backpacking Base Layers: Quick Navigation
Smartwool Merino 250 | Warmest Layer
Patagonia Capilene Cool Daily | Best Lightweight Synthetic
REI Co-op Lightweight | Most Affordable
Icebreaker Merino 200 Oasis| Best-Looking
Meriwool Lightweight Base Layers| Best Budget-Friendly Merino
REI Co-op Silk Long Underwear | Best Ultralight
Features to Look for in the Best Backpacking Baselayers
The ability to breathe and wick sweat efficiently, keeping you comfortable and non-clammy, is one of your baselayer’s most critical functions—particularly for active baselayers (those you’ll be wearing next to your skin while hiking). Fabric type, weight, ventilation features, and fit will determine how breathable/wicking your baselayers are. Ensure your baselayers fit close to the skin (without being uncomfortably tight) to maximize wicking efficiency.
Silk: Silk is the most ultralight material. It’s warm for the weight, but it’s not very breathable or durable. Probably better suited for sleeping clothes than activewear.
Merino wool: Merino is exceptionally soft and does a great job retaining warmth even when wet. It’s also naturally anti-odor, flame retardant, and moisture-wicking.
Synthetic: Merino and silk are both more expensive than synthetic fabrics (usually polyester or nylon, sometimes blended with elastane to make them stretchy). Synthetics are durable and are almost as breathable and moisture-wicking as merino wool. They don’t have the same next-to-skin comfort, though, and can reek something awful after you’ve worn them for a few days.
Fabrics are available in different densities/weights depending on how warm you want them to be. Merino, for instance, is commonly sold in 100-250-weight varieties, meaning 100-250 grams per square meter (gsm). Less-than-200 gsm merino is thinner, lighter, and more suitable to warm conditions. Anything above 200 gsm is ideal for cooler weather.
Anecdotally, 200+ gsm merino also seems to be less susceptible to insect damage. On more than one occasion, we’ve had 150 and 250 gsm merino garments in the same drawer and only found moth damage in the 150 gsm garments.
Some ultralight enthusiasts will use heavyweight baselayer tops as their midlayer in warm weather, replacing a heavier and bulkier garment like a fleece.
Some baselayers have thinner materials or a more open weave in hot, sweaty areas like the armpits and behind the knees to improve breathability.
Merino wool is naturally antimicrobial, but some synthetic baselayers feature an antimicrobial treatment meant to inhibit odors. Anti-stink properties are nice to have but probably not a determining factor for most hikers since hiker funk will eventually overwhelm any garment’s limited odor-fighting ability.
Thumb Loops, Pockets, Zippers
Thumb loops: Keep your sleeves down around your wrists and get some coverage of part of your hand—great for cold conditions.
Pockets: One or two small pockets, or a kangaroo pocket, can store small items or warm up your hands.
Zippers: Quarter-zip tops give you more temperature control because you can unzip to vent heat as needed.
Base Layers by Season
Winter: While hiking, wear thicker (200+ gsm) leggings and a long-sleeve crewneck or quarter-zip top. Opt for something stretchy that will hug your skin without restricting motion. Bonus points if it’s breathable/moisture-wicking. You’ll probably layer a fleece and a set of rain, wind, or hiking pants on top of your baselayers this time of year for additional warmth. Change into a second, dry set of thick base layers (still 200+ gsm) when you get to camp. These should still sit close to your skin to maximize warmth, but breathability and mobility aren’t as important as you’ll just be sleeping in them.
Spring and Fall: Wear your active (stretchy, breathable) base layers as your outer layer. Whether to go with thin layers or thick depends mainly on the trail you’ll be hiking and whether you run hot or cold. Again, bring a dry, thick pair of base layers to sleep in since nights will still be chilly.
Summer: A lightweight, breathable shirt and shorts (or hiking pants) will be fine for most hikers If you want dedicated sleep clothes, ultralight silk base layers make great backpacking PJs.
Do I really need fancy technical baselayers?
Nope. Technical, performance hiking baselayers can get scary expensive—think $50-$100 or more for a single garment. But you can find an inexpensive, lightweight set of synthetic baselayers in the Active Wear section of any big box store or even at a thrift store. There is a performance difference between inexpensive exercise apparel and expensive hiking clothes, but it’s sometimes overstated. Besides, after a few months on trail, your outfit will be reduced to stinky rags regardless of cost.
About Our 2021 Picks
For the sake of internal consistency, all specs listed are for a men’s medium unless otherwise stated. We’re focusing on long-sleeve crew tops for the same reason, but all of the listed baselayers are available in bottoms as well, and many also come as hoodies, half-zips, or short-sleeve tees. As we stated above, it’s OK to use any pair of synthetic long johns from a thrift or big box store as baselayers if you’re on a budget. However, we curated this list for products that boast exceptional breathability, durability, and/or comfort.
The Best Backpacking Baselayers of 2021
Smartwool Merino 250 | Warmest Backpacking Baselayer
Materials: 100% merino wool (250 gsm)
Weight: 9.3 oz
In addition to featuring awesome colors and patterns, Smartwool’s tight, interlock-knit, 100% merino construction makes this an incredibly warm, soft baselayer. It breathes incredibly well, is naturally odor-inhibiting, and features no-chafe flatlock seams and ribbed elbows for maximum mobility.
Patagonia Capilene Cool Daily | Best Synthetic Backpacking Baselayers
Materials: Synthetic (50% polyester, 50% recycled polyester jersey)
Weight: 3.8 oz
Stretchy, UPF-50+ fabric keeps you cool and protected on hot days on trail. The Patagonia Capilene Cool Daily line is perfect for sunny summer hiking: it’s uber comfortable, dries in a flash, keeps chafe-inducing seams to a minimum, and even has a Polygiene odor treatment to help counteract the unholy stench for which sweaty polyester is usually notorious. Patagonia makes an effort to sustainability in their product line, and their Capilene baselayers are no exception. This shirt, for instance, uses 50% recycled polyester and has a Fair Trade certification that indicates ethical labor practices.
REI Co-op Lightweight Base Layer | Most Affordable Base Layer
Material: Synthetic (92% polyester, 8% spandex)
Weight: 6.1 oz
REI’s take on the synthetic baselayer is suitable as activewear, with UPF 50+ sun protection and a variety of comfort and mobility-enhancing features. These include raglan sleeves, gusseted underarms, four-way stretch, and flat seams that minimize chafing. It fits looser than many baselayers, which may reduce its breathability and moisture-wicking properties.
Icebreaker Merino 200 Oasis | Best Looking Backpacking Baselayers
Materials: 100% merino wool jersey (200 gsm)
Weight: 7.9 oz (men’s large)
Icebreaker and Smartwool baselayers are comparable in most respects, but if you favor a trimmer, more athletic fit, Icebreaker is the way to go. It also has a drop tail hem (more bum coverage), which adds warmth and reduces the risk of your shirt riding up under your pack. For both of these reasons, we think this Icebreaker offering is a better active layer than the Smartwools. The Merino 200 Oasis also features gusseted underarms, flatlock seams, and offset shoulder seams to reduce pack strap chafing. Two hundred-weight merino is a little lighter and airier than Smartwool’s 250, as well, ideal if you’re looking for a later with in-between warmth.
Meriwool Lightweight Base Layer | Most Affordable Merino Baselayers
Materials: 100% merino wool (180 gsm)
Weight: not available
Hikers love to sing the praises of merino wool—warm, wicking, breathable, odor-resistant—but sadly, thriftiness is generally not among the yarn’s many miraculous qualities. For many hiker trash, the extreme cost of merino wool is a steep barrier. Enter Meriwool, a line of 100% merino baselayers that cost roughly half as much as most competitors. Their light (180-weight) baselayer is the cheapest option and still sports thoughtful touches like raglan sleeves and a wide range of sizes.
REI Co-op Silk Long Underwear | Best Ultralight Backpacking Baselayers
Materials: 100% pure silk jersey
Weight: 2.9 oz
REI’s silk long johns feel amazing next to your skin and are remarkably warm for such a thin, sheer layer. You can wear them under your hiking clothes for a boost in warmth, but they’re not very breathable or durable, so we recommend using them as luxurious camp PJs instead. Also available in bottoms.
Why should you trust us?
Because we’re so incredibly intelligent, of course! Attractive, too. (Not to mention extremely humble).
But if that isn’t enough to impress you, there’s also the fact that everyone who contributed to this article is an experienced thru-hiker with thousands of on-trail miles under their belt. We’re gear nerds who love putting our equipment to the test on trails long and short, and we’ve tested dozens of baselayers in pursuit of comfier backcountry days.
Moreover, we do our best to stay plugged into the trail community’s gear preferences (we are definitely those obnoxious people on trail who always want to know what everyone else is packing). That means our picks for the best backpacking baselayers aren’t just our opinions: they’re based on years of feedback from the thru-hiking community.
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