Best Long Underwear of 2025

Reasons to Buy

• Soft and comfortable merino wool material
• Keeps user warm in low temperatures
• Moisture-wicking capabilities
• Odor-resistant compared to other base layers
• Top-notch breathability allowing good ventilation

Reasons to Avoid

• Somewhat expensive relative to other base layers
• May feel a bit tight for some users
• Durability reported as lower compared to synthetic layers

The Smartwool Merino 250 Base Layer Bottoms have been impressing those in the camping, backpacking, and climbing communities for quite some time now. This solid set of long underwear has garnered a good reputation for a few key factors.

One of the most consistently praised features is the superior warmth these provide. Made from 100% Merino wool, you can count on a cozy and comfortable fit even on the coldest of hiking trails. Many customers have reported that these are ideal in winter weather conditions, providing just the right amount of insulation and warmth.

Yet it's not just the warmth these bottoms dish out that's got everyone talking. They're also applauded for their comfort, largely attributed to the interlock knit style used in their construction. This allows for a certain level of stretch and flexibility, perfect for those more challenging climbs.

Customers have also highlighted the base layer's excellent moisture management. Whether you're on a long trek or pushing yourself on a climb, sweat can be an unavoidable consequence. However, the Smartwool Merino 250 Base Layer Bottoms are designed to wick away moisture effectively, keeping you dry and enhancing your overall comfort experience.

While generally considered a top-notch choice, they're not without the occasional criticism. For instance, some customers have raised concerns over the sizing and recommended checking the size guide carefully before purchase. Others weren't thrilled with the price tag, viewing these bottoms as a little on the expensive side.

But all in all, the Smartwool Merino 250 Base Layer Bottoms continue to dominate the long underwear game. The combination of warmth, comfort, and superb moisture management often outweigh the few criticisms. Users have shared time and again how much they appreciate having these in their backpack on chilly adventures, and how they have become a key component of their outdoor kit.

Reasons to Buy

• Comfortable fit with strong elasticity
• Excellent warmth-to-weight ratio
• Durable with reinforced stitching
• Superior moisture-wicking and breathability
• Great odor resistance

Reasons to Avoid

• Costlier than comparable options
• Not the most stylish design
• May not be ideal for extreme cold

Arc'teryx Men's Rho LT Bottom is a solid option for anyone seeking long underwear that marries both comfort and performance. Made to insulate and regulate body temperature, these bottoms are a crowd-pleaser among outdoor enthusiasts, climbers and hiker types alike.

Right off the bat, reviewers love the snug, warm fit that the Rho LT Bottom offers. Thanks to the Torrent™ polyester and elastane blend material, these bottoms are both stretchy and breathable; an important combo for all-day wear during a range of activities.

Many folks online have praised the design and fit of the Men's Rho LT Bottom. Users noted that unlike other long underwear, they don't ride up or bunch, but fit snugly around the leg and give a seamless look under pants. It's a detail many customers appreciated and often referred to as a 'great fit.'

Described as 'lightweight', but not skimpy on the heat, the Arc'teryx Men's Rho LT Bottom has been praised for its thermal capabilities. Reviewers shared their experiences of weathering even the most bone-chilling temperatures in these - a testament to the quality Arc'teryx promises.

One drawback some reviews mentioned is the product's price point. It's a bit on the higher end compared to others in the market. But a large chunk of users say it's a worthy investment for the warmth, comfort, and durability the Rho LT Bottom provides.

In terms of maintenance, reviewers found these bottoms easy to clean - they're machine washable and dry quickly. However, a few users observed that they may pill slightly after frequent washing.

Another positive aspect users often commented on is the odor-resistance of these bottoms. According to multiple reviews, the Rho LT Bottom seems to keep the 'stink factor' at bay, even after a few days of wear, which is definitely a big plus for multi-day hikers.

All-in-all, the Arc'teryx Men's Rho LT Bottom comes highly recommended by many customers for its comfort, insulation, and quality. But keep in mind the slightly higher price tag and potential for minor pilling with frequent laundering.

Reasons to Buy

• Superior warmth
• Excellent breathability
• Functionally stretchy
• Sustainable materials

Reasons to Avoid

• On the pricier side
• Not as durable with heavy use

The Patagonia Capilene Air Bottoms deserve recognition as a top-notch choice for men's long underwear. These bottoms are truly in a league of their own in terms of both comfort and functionality. Made from an innovative blend of recycled polyester and merino wool-based yarn, they're designed to be soft, warm, and breathable. They're an environmentally-friendly option for the more conscious consumer.

When it comes to warmth, numerous customer reviews highlight their effectiveness even in bone-chilling temperatures, beating some of the heftier options hands down. Their sleek, lightweight design coupled with their powerful insulation stake their claim as a strong competitor to your traditional, chunkier long johns.

Talking about breathable/ventilation properties, buyers frequently mentioned their quick-drying capabilities. Sweat doesn't stand a chance, being quickly whisked away from your skin, helping maintain a dry and comfortable base layer even during strenuous activities. Also worth mentioning is the nature-centric pattern, loved by many for bringing a touch of style to their outdoor gear.

Furthermore, customers love the stretchiness you get with these bottoms. Whether you're hiking, climbing, or lounging by the campfire, it's clear this balanced elasticity, backed up by numerous reviews, not only provides freedom of movement but also ensures a form-fitting shape after repeated use.

However, every product has its downsides and the Patagonia Capilene Air Bottoms are no exception. Although the breathability and thermal capacity are praised, several customers have indicated a small snag - these capilene bottoms aren't the best performers in terms of toughness. Some users noticed minor wear and tear issues after extensive use, especially in high friction areas.

Another common issue mentioned by customers pertains to the price tag. These bottoms are indeed not the most budget-friendly option out there. However, many of those who took the plunge vouched for the quality and overall performance, stating they were worth every penny.

In terms of sizing, opinions vary. Some find that these bottoms run slightly larger than expected, while others find them true to their size. It seems a good idea to try these on before making a purchasing decision, if possible.

Reasons to Buy

• Affordable price
• Good warmth-to-weight ratio
• Effective moisture wicking
• Odor resistance

Reasons to Avoid

• Not the most durable
• Fit might be too loose for some

The REI Co-op Midweight Bottoms are a popular choice for many outdoor enthusiasts looking for a budget-friendly option without skimping on functionality. As their name suggests, these bottoms are midweight, making them versatile for various weather conditions; from chillier morning hikes to comfortable wear under a pair of ski pants.

This product has a user-friendly blend of polyester and elastane that provides a nice balance between warmth, breathability and elasticity. Due to their stretchiness, users have appreciated the close but comfortable fit that doesn't hinder movement on long treks or intense climbs.

One thing that's been praised by many customers is the design of these bottoms. Featuring flatlock seams, these reduce chafing which can be a real nuisance on more extended trips. The waistband is also comfortable and doesn't dig in, an attribute appreciated by individuals with varying waist sizes.

In terms of durability, these bottoms seem to hold up pretty well. Users have mentioned that after several washes the fabric retains its shape, while the waistband and ankles maintain their elasticity. However, some have mentioned mild pilling in areas of high friction over time.

On the downside, some customers have noted that the REI Co-op Midweight Bottoms run a bit long, which could be a hurdle for shorter individuals. And while they’ve received positive feedback on their thermal capabilities, they might not provide enough insulation for extreme cold conditions.

In the end, the REI Co-op Midweight Bottoms stand out as worthwhile for their cozy fit and affordability. Despite a few minor faults, they remain a resounding favourite among outdoor adventurers on a budget.