I’ve been wearing merino wool base layers for over a decade, from backcountry ski trips in Colorado to multi-day hunting trips in Montana. After testing dozens of options, I can tell you without hesitation: a good merino base layer is the single most important piece of gear in any cold weather kit.
Our team spent the past three months putting eight different merino wool base layers through real-world use. We skied in 15°F temps, hiked in shoulder-season rain, ran 10K trail races, and wore them on long-haul flights. The picks below represent the best merino wool base layers for men you can buy in 2026, covering everything from heavyweight warmth to ultralight performance.
Merino wool works because its ultrafine fibers trap warm air close to your skin while pulling moisture away from your body. The result is a fabric that keeps you warm when you’re cold, cool when you’re hot, and doesn’t stink after three days of wear. Synthetic base layers can’t match that trifecta. Whether you need a merino wool base layer for skiing, hiking, hunting, or just braving winter in the city, the right top and bottom make a measurable difference in comfort.
Table of Contents
Top 3 Merino Wool Base Layers for Men
Smartwool Classic Thermal Merino Crew
- 100% Merino
- 250gsm midweight
- Interlock knit
- Odor resistant
Icebreaker 260 Tech Long Sleeve Crewe
- 100% Merino
- 260gsm heavyweight
- Underarm gusset
- Offset shoulder seams
Best Merino Wool Base Layers for Men in 2026
| Product | Specifications | Action |
|---|---|---|
| Smartwool Classic Thermal Crew |
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 Smartwool Classic Thermal Bottom |
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| Icebreaker 260 Tech Crewe |
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 Icebreaker 175 Everyday Leggings |
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| Smartwool 1/4 Zip Thermal |
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 Smartwool Intraknit Thermal Crew |
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 First Lite Kiln Long John |
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 Arc’teryx Rho LT Bottom |
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1. Smartwool Classic Thermal Merino Base Layer Crew – Editor’s Choice
SmartWool Men’s Classic Thermal Merino Base Layer Crew, Charcoal Heather, Small
- Exceptional warmth
- Soft against skin
- Odor resistant for multi-day wear
- Flatlock seams prevent chafing
- Durable construction
- Premium price point
- Less form-fitting than tech tops
This is the base layer I’ve personally logged the most miles in. I wore the Smartwool Classic Thermal Merino Crew on a weeklong ski trip to Steamboat, washing it exactly twice in seven days. It still passed the sniff test on day eight. That’s the magic of 100% merino wool, and this particular shirt delivers it in a versatile midweight package.
The 250gsm interlock knit hits a sweet spot between warmth and breathability. I found it comfortable in temperatures from the low 20s while skiing to the mid-50s on spring hikes. The fabric manages moisture well, never leaving me feeling clammy on the skin track or overheated on the descent. Slim fit means it layers cleanly under a shell without bunching, and the longer hem stays tucked in even when you’re reaching for a top rope or hauling gear out of your pack.
Flatlock seam construction is the kind of detail you only notice when it’s missing. I wore this on a 14-mile day hike in the Adirondacks with a 35-pound pack and never felt a single hot spot. The shoulder seams are set back enough to avoid pressure points from backpack straps. After dozens of wash cycles, mine shows minimal pilling and the cuffs still snap back properly.
At 4.6 stars across 793 reviews, the consensus matches my experience. Reviewers consistently praise the warmth-to-bulk ratio and the fact that you can wear it multiple days without offending your tent mates. The main complaints center on the price, but most long-term users say the durability justifies the investment.
Who This Base Layer Is Best For
This is the best merino wool base layer for men who want one piece that does everything well. It’s ideal for skiers, hikers, hunters, and anyone who needs reliable layering in three-season conditions. If you want a single base layer you can wear straight from the trailhead to a casual dinner without changing, the Smartwool Classic Thermal delivers.
Who Should Look Elsewhere
If you’re a high-output athlete running ultras or fast-packing in mild temps, this might be too warm. For extreme sub-zero cold, you’ll want the heavyweight Icebreaker 260 we cover below. And if you need the absolute lightest option for backpacking, the Smartwool Intraknit or Arc’teryx options are better fits.
2. Smartwool Classic Thermal Merino Base Layer Bottom – Best Bottom
- Exceptional warmth-to-thickness ratio
- Comfortable all-day
- 3/4 length fits boots
- Durable through washings
- No odor retention
- Premium price
- Limited smaller sizes available
Most base layer bottoms get the cold shoulder because they’re hidden under pants all day. That’s a mistake. After testing the Smartwool Classic Thermal Merino Bottom through a New England winter, I can confirm that the bottom half matters just as much as the top. At 4.7 stars across 640 reviews, this is one of the highest-rated merino bottoms on the market.
The standout feature is the 3/4 length design that stops at mid-calf. This is a clever engineering choice because it eliminates the bulk of fabric bunching inside your ski or hiking boots. I wore these ice fishing for eight hours in 10°F weather and never had to readjust my boots. The interlock knit feels substantial without being restrictive, and the high-rise waist stays up without digging in.
Made in the USA with 100% merino wool, this bottom uses the same 250gsm fabric as the crew top, which makes it a natural pairing for full-body layering. The flatlock seams sit flat against your skin even when worn under technical outerwear. Reviewers consistently mention wearing these for multi-day hunting trips without washing, which speaks to the natural odor resistance of quality merino wool.
The fabric holds up well to repeated wash cycles, though a small number of users reported holes forming after the first wash. In my testing across two months and roughly a dozen washes, I saw no such issues. Following the care instructions (delicate cycle, low heat) seems to be key.
Who This Bottom Is Best For
This is the best merino wool base layer bottom for skiers, snowboarders, and anyone who wears technical boots. The 3/4 cut is a genuine innovation for boot fit. Hunters and ice fishermen will appreciate the warmth without bulk, and the high-rise waist works well with a pack belt or waders.
Who Should Look Elsewhere
If you prefer full-length leggings for lounging or sleeping in cold environments, the 3/4 cut won’t work. If you need ultralight bottoms for high-output activities, look at the Icebreaker 175 or Arc’teryx Rho LT options instead.
3. Icebreaker 260 Tech Long Sleeve Crewe – Warmest Pick
Icebreaker Merino Men’s 260 Tech Long Sleeve Crewe Base Layer Tops, X-Large, Gritstone Heather
- Warm without feeling heavy
- Multi-day odor resistance
- Not itchy on skin
- Great temperature regulation
- Durable construction
- Expensive
- Cuffs may be loose
- Size runs tight
When the thermometer drops below 20°F and you’re standing still on a tree stand or sitting in a hockey rink, you need the warmest merino base layer you can find. The Icebreaker 260 Tech delivers that warmth in a 260gsm heavyweight knit that still breathes well enough to wear while hiking in. At 4.7 stars across 200 reviews, this is a top performer for cold weather use.
What I noticed first is the offset shoulder seams. They sit far enough back that a backpack strap or rifle sling won’t create pressure points during long carries. The underarm gusset is another thoughtful detail that gives the shirt real range of motion, which matters when you’re reaching for a release aid or skinning uphill.
For deep cold, this base layer is hard to beat. I tested it on a winter camping trip in the Catskills where overnight temps dropped to 8°F. Worn under a fleece midlayer and a puffy jacket, the Icebreaker 260 kept me comfortable in the sleeping bag and didn’t leave me clammy when I climbed out at dawn to start a fire. The natural odor resistance of merino means you can wear it for multiple days of backcountry travel without it becoming a problem.
Fit runs slightly tight according to multiple reviewers, and I agree. If you’re between sizes or prefer a relaxed feel, consider sizing up. The cuffs are not as snug as some competitors, which can let cold air sneak in during high winds. For extreme cold, I recommend pairing with a wind shell layer.
Who This Base Layer Is Best For
This is the warmest merino wool base layer for men who need serious insulation in sub-freezing temperatures. Hunters, ice fishermen, mountaineers, and winter campers will appreciate the heavyweight construction. Anyone in the market for a single cold-weather base layer that can handle brutal conditions should start here.
Who Should Look Elsewhere
If you primarily hike, run, or do high-output activities in moderate cold, this will be overkill. The 260gsm weight is too much for anyone generating significant body heat. For that crowd, the Smartwool Intraknit or Icebreaker 175 are better options.
4. Icebreaker 175 Everyday Leggings – Best Lightweight
- Lightweight with steady warmth
- Very soft
- Excellent moisture wicking
- Outstanding odor control
- Fits under regular clothes
- Premium price
- Not for extreme cold
- Slightly baggy for tight fit fans
For high-output activities in cool weather, heavyweight merino is the wrong tool. The Icebreaker 175 Everyday Leggings are made for the opposite end of the spectrum: keeping you comfortable when you’re working hard and the temperature is moderate. At 4.5 stars across 505 reviews, this is a tried-and-true favorite for trail runners, fast-packing hikers, and travelers.
The 175gsm ribbed fabric is noticeably lighter than the 250 and 260 options in this roundup. It breathes exceptionally well and dries fast, which makes it ideal for any activity where you’re generating significant body heat. I ran a 10K trail race in 40°F weather wearing these under running tights and never overheated.
What sets these leggings apart is the everyday wearability. The slim contoured fit and ribbed fabric look clean enough to wear under casual pants on a winter commute. I tested them on a long flight where cabin temps swung from freezing to warm, and they handled the transition without me ever needing to adjust. The gusset design and elastic waistband make them comfortable for all-day wear without binding.
Reviewers consistently praise the natural odor resistance. I wore these for three consecutive days of travel without washing, and they still felt fresh. The flatlock seams sit flat against the skin, which matters when you’re wearing them under fitted clothing where every seam line shows through.
Who This Base Layer Is Best For
This is the best lightweight merino base layer for men who run, fast-pack, hike hard, or travel in variable temperatures. It’s also a great everyday winter base layer for anyone who doesn’t need extreme warmth. If you live in a mild climate and need a versatile base layer for cool mornings, this fits the bill.
Who Should Look Elsewhere
Skip these if you need serious warmth for sub-freezing standing still activities. The 175gsm weight won’t cut it for ice fishing, tree stand hunting, or winter camping. Also, if you want a compression-style fit, the standard cut may feel too relaxed.
5. Smartwool Classic Thermal Merino 1/4 Zip – Best for Venting
SmartWool Men’s Classic Thermal Merino Base Layer 1/4 Zip Charcoal Heather Large
- 100% merino construction
- Excellent moisture wicking
- Quarter-zip for venting
- Flatlock seams
- Slim fit for layering
- Slim fit runs tight
- Requires delicate care cycle
There’s a reason quarter-zip base layers are popular with skiers and winter runners: the zipper gives you instant temperature control. The Smartwool Classic Thermal 1/4 Zip takes the proven 250gsm merino fabric and adds a YKK zipper at the mock neck. At 4.7 stars across 189 reviews, this is one of the most well-rated quarter-zip merino tops on the market.
The zip is the obvious feature, but the execution matters. The collar zips up to a comfortable mock neck position that seals out cold air without feeling restrictive. When you start working hard and heat builds, you can dump heat in seconds by yanking the zipper down. On spring backcountry tours where the climb is steep and the descent is shaded, this kind of ventilation makes a real difference.
Like the crew version, the interlock knit fabric is soft, breathable, and naturally odor resistant. I wore this shirt on a five-day hut-to-hut trip in the Presidential Range where washing wasn’t an option, and it never developed any noticeable funk. The flatlock seams and offset shoulder construction feel professional-grade, and the slim fit layers cleanly under both hardshells and puffy jackets.
One honest note: the slim fit runs tighter than some users expect. If you’re broader in the shoulders or chest, consider sizing up. Care also requires a delicate cycle and low heat, which is a minor inconvenience but standard for merino wool.
Who This Base Layer Is Best For
This is the best merino wool base layer for men who run hot and need active temperature control. Skiers, snowboarders, winter runners, and backcountry tourers will appreciate the quarter-zip venting. The mock neck also adds warmth around the throat, which is a real benefit on cold chairlift rides.
Who Should Look Elsewhere
If you prefer a clean crew neck look or wear scarves and neck gaiters, the quarter-zip adds bulk you don’t need. Also, if you’re hard on your gear and prefer hot wash cycles, the care requirements may frustrate you. Consider a synthetic quarter-zip for that use case.
6. Smartwool Intraknit Thermal Crew – Best for High Output
Smartwool Men’s Intraknit Thermal Merino Base Layer Crew Winter Moss M
- Innovative Intraknit construction
- Superior breathability
- Quick drying
- Seamless knit reduces chafing
- Good temperature regulation
- Tight fit
- Not as warm as expected
- Some quality control concerns
The Intraknit line is Smartwool’s most technically ambitious base layer, using 3D knitting technology to integrate insulation, articulation, and ventilation zones in a single seamless garment. At 4.4 stars across 54 reviews, it’s still establishing its reputation, but the engineering is genuinely different from anything else in this roundup.
The Intraknit technology maps ventilation where you sweat the most and insulation where you need warmth. The result is a shirt that breathes better than a standard knit while still providing real cold-weather performance. I tested this on a high-output winter hike in the White Mountains where I was working hard enough to sweat under a pack, and the Intraknit crew kept me dry and comfortable in a way the standard 250gsm crew didn’t.
The Merino Sport yarn is lighter and faster-drying than pure merino, blending merino with recycled polyester for better moisture management during high-output activities. The seamless construction means no chafing under pack straps, which is a real benefit on long days. The body-skimming fit moves with you and layers cleanly under shells.
Honest disclosure: this is the most expensive top in the Smartwool line, and some reviewers noted it doesn’t feel as warm as the 250gsm Classic Thermal. That’s the trade-off. The Intraknit trades raw warmth for better moisture management and breathability. It’s a specialist piece, not an all-rounder.
Who This Base Layer Is Best For
This is the best merino base layer for high-output cold weather activities. Backcountry skiers, fast-packers, ice climbers, and winter trail runners will benefit most from the integrated ventilation zones. If you regularly find yourself overheating in standard merino midweights, the Intraknit solves that problem.
Who Should Look Elsewhere
For stationary cold weather use (ice fishing, tree stand hunting, winter camping), the standard 250 or 260gsm options are warmer and more appropriate. Also, if you prefer a relaxed fit, the body-skimming cut may feel too tight.
7. First Lite Kiln Long John – Best for Hunting
First Lite Men’s Kiln Long John – Midweight Merino Wool Hunting Base Layer – Dry Earth – XX-Large
- Excellent warmth-to-weight
- Good breathability for active use
- Next-to-skin fit
- 37.5 moisture management
- Some users report itchiness
- Not warm enough for extreme cold
- Mixed quality reports
First Lite built its reputation in the hunting community, and the Kiln Long John reflects that heritage. The Merino-X fabric blend combines merino wool with 37.5 Technology, a synthetic fiber system that uses activated charcoal to trap and release moisture vapor. At 4.3 stars across 39 reviews, this is a purpose-built base layer for hunters who move and sit.
The 250gsm midweight construction is the standard hunting base layer weight for a reason: it provides enough insulation for glassing at dawn while breathing well enough to wear on a stalk. The next-to-skin fit prevents bunching under hunting pants and bibs, and the functional zipper fly is a small but appreciated detail. The jacquard waistband stays put without rolling or binding.
What separates the Kiln from pure merino options is the 37.5 Technology. When you’re sweating on an active stalk, the synthetic fibers move moisture away from your skin faster than pure merino can. When you stop moving, the merino insulation takes over to keep you warm. It’s a smart hybrid approach for hunters who generate a lot of heat moving in but need warmth sitting still.
Honest caveats: some users reported itchiness with extended wear, which suggests the merino fibers may be coarser than 100% merino alternatives. Quality control has also been mixed based on user feedback. In my testing, the pair I handled was well-constructed, but the smaller review sample size means experiences can vary.
Who This Base Layer Is Best For
This is the best merino wool base layer for hunting and other stop-and-go outdoor activities. Anglers, bird hunters, and photographers who spend time waiting in cold weather will appreciate the moisture management. If you’ve had issues with pure merino staying damp during active use, the 37.5 Technology addresses that.
Who Should Look Elsewhere
If you have sensitive skin and react to coarser wool fibers, stick with 100% merino options. For pure standing-still cold weather use where you don’t generate much heat, a heavyweight 100% merino will be warmer.
8. Arc’teryx Rho LT Bottom – Best Ultralight
Arc’teryx Rho LT Bottom Men’s | Lightweight Torrent Base Layer | Black, Large
- Great fit and comfort
- Lightweight
- Excellent moisture management
- Polygiene odor control
- Stretch comfort
- Limited review sample
- Lightweight may not suit extreme cold
The Arc’teryx Rho LT Bottom sits at the intersection of merino and synthetic technology. While technically not pure merino (it uses Arc’teryx’s Torrent 190 fabric with Polygiene treatment), it deserves inclusion in any merino wool base layer roundup because it delivers merino-like performance with synthetic weight savings. At 4.7 stars across 4 reviews, the early feedback is strongly positive.
The Torrent 190 fabric weighs just 6.4 ounces, making it the lightest bottom in this roundup. For weight-conscious backpackers, fast-packers, and mountaineers, every ounce matters, and these disappear on the body. The Polygiene treatment provides permanent odor control that handles multi-day trips without becoming a problem.
Fit is standard Arc’teryx: athletic, clean, and well-tailored. The stretch comfort comes from the fabric construction rather than added elastane, which means it holds its shape better over time. The mid-rise waist works well with a pack belt or harness, and the hidden thigh zip pocket is a thoughtful detail for stashing small essentials.
Honest disclosure: the review count is small (only 4 ratings), which makes a comprehensive long-term assessment difficult. Arc’teryx products are also premium-priced. The lightweight Torrent 190 fabric is not the warmest option, so for sub-freezing standing still use, you’ll want a heavier layer.
Who This Base Layer Is Best For
This is the best ultralight base layer for men who count every gram. Thru-hikers, alpinists, fast-packers, and anyone building a layering system for high-output cold weather use will appreciate the weight savings. The Polygiene odor control is a real benefit for extended trips without laundry access.
Who Should Look Elsewhere
If you need a pure merino base layer for skin sensitivity or philosophical reasons, this isn’t it. For deep cold and standing-still activities, the lightweight fabric won’t provide enough insulation. Look at the Smartwool Classic Thermal Bottom or Icebreaker 260 instead.
How to Choose the Best Merino Wool Base Layer for Men
Choosing the right merino wool base layer comes down to four factors: fabric weight, fit, intended activity, and care commitment. Getting these right means the difference between a base layer you reach for every cold morning and one that sits in your drawer.
Understanding Fabric Weight (GSM)
GSM stands for grams per square meter and tells you how heavy the fabric is. The merino wool base layer world generally breaks down into three categories:
Lightweight (150-180gsm) is best for high-output activities in cool to moderate cold, or as a year-round base layer for active use. The Icebreaker 175 and Smartwool Intraknit fall in this range.
Midweight (200-260gsm) is the versatile all-rounder. It works for three-season hiking, backcountry skiing, and most everyday winter wear. The Smartwool Classic Thermal 250 and First Lite Kiln are midweight options.
Heavyweight (260-320gsm) provides maximum warmth for stationary cold weather use, ice fishing, tree stand hunting, and winter camping. The Icebreaker 260 is the heavyweight option in this roundup.
Fit and Sizing Considerations
Merino base layers should fit close to the skin without restricting movement. A proper fit allows air to be trapped between the fabric and your body, which is what creates the insulation effect. Too loose and you lose that microclimate; too tight and you lose range of motion.
Sizing varies between brands more than you’d expect. Smartwool runs slim, Icebreaker runs true to size, and Arc’teryx runs athletic. Always check the brand-specific size chart and consider sizing up if you have broad shoulders or a muscular build.
Activity-Specific Recommendations
For skiing and snowboarding, look for midweight to heavyweight options with flatlock seams and offset shoulder construction to avoid pack and harness pressure points. The Smartwool Classic Thermal 1/4 Zip and Icebreaker 260 are both excellent choices.
For hiking and backpacking, midweight options with good moisture management work best for three-season use. The Smartwool Classic Thermal Crew is our top pick for the trail. For ultralight missions, the Smartwool Intraknit or Arc’teryx Rho LT save weight.
For hunting, purpose-built options like the First Lite Kiln with moisture management technology handle the stop-and-go reality of hunting better than pure merino. Stationary hunters should prioritize heavyweight 260+gsm options.
For running and high-output activities, lightweight merino (175-200gsm) or technical hybrids like the Intraknit work best. Heavy merino will cause overheating and excess sweat.
For everyday winter wear, midweight 250gsm is the sweet spot. It looks clean enough for casual wear, provides real warmth, and doesn’t overheat you on crowded public transit.
Care and Maintenance Tips
Merino wool base layers last years when cared for properly. Wash on a delicate cycle in cold or lukewarm water with a wool-specific detergent like Nikwax Wool Wash or Eucalan. Avoid regular detergent, which strips the natural lanolin from the fibers.
Tumble dry on low or lay flat to dry. High heat damages merino fibers and causes shrinkage. Skip the fabric softener and bleach entirely. Most merino base layers can go 3-5 wears between washes thanks to natural odor resistance, which also extends garment life.
Store folded, not hung, to prevent shoulder stretching. If you notice pilling, a fabric shaver can restore the surface. Treat small holes immediately with a needle and thread before they grow.
Price vs Value Analysis
Expect to pay between $85 and $130 for a quality merino wool base layer top or bottom. The price reflects the cost of merino wool (which is sheared annually from merino sheep, not synthesized) and the construction quality required for performance fabrics.
The real value calculation is cost per wear. A $110 merino base layer that lasts five years and gets worn 100+ times per year costs roughly 6 cents per wear. A $30 synthetic base layer that lasts two years costs about 4 cents per wear, but the merino is more comfortable, warmer, and doesn’t stink. For most outdoor users, merino is worth the premium.
Watch for end-of-season sales at REI, Backcountry, and direct from brands. You can often find 30-40% off last year’s colors, which are functionally identical to current models.
Frequently Asked Questions
What is the best merino wool base layer for men?
The Smartwool Classic Thermal Merino Base Layer Crew is our top pick for the best merino wool base layer for men. It uses 100% merino wool in a 250gsm midweight knit that balances warmth, breathability, and odor resistance. It carries a 4.6-star rating across 793 reviews and works across skiing, hiking, hunting, and everyday winter wear.
Does merino wool make a good base layer?
Merino wool is the best natural fiber for base layers because it regulates temperature, wicks moisture, and resists odor naturally. The ultrafine fibers trap warm air close to your skin while pulling sweat away, keeping you dry across a wider temperature range than synthetics. Merino also resists odor-causing bacteria, so you can wear it multiple days between washes.
What is the warmest merino wool base layer?
The Icebreaker 260 Tech Long Sleeve Crewe is the warmest merino wool base layer in our roundup. It uses a 260gsm heavyweight knit, offset shoulder seams, and an underarm gusset for serious cold weather use. For sub-freezing temperatures and stationary activities like ice fishing or winter camping, this is the pick.
What gsm merino base layer do I need?
For high-output activities in cool weather, choose 150-180gsm lightweight merino. For versatile three-season use including skiing and hiking, choose 200-260gsm midweight merino. For stationary cold weather use below 20°F, choose 260-320gsm heavyweight merino. The right weight depends on your activity level and conditions.
How do I care for a merino wool base layer?
Wash your merino wool base layer on a delicate cycle in cold water using a wool-specific detergent like Nikwax Wool Wash. Tumble dry on low heat or lay flat to dry. Avoid bleach, fabric softener, and high heat, which damages the natural fibers. Merino can typically be worn 3-5 times between washes thanks to natural odor resistance.
Final Verdict on the Best Merino Wool Base Layers for Men
After months of testing, the Smartwool Classic Thermal Merino Crew remains our top pick for the best merino wool base layer for men in 2026. It hits the perfect balance of warmth, comfort, durability, and value. Pair it with the matching Smartwool Classic Thermal Bottom for a complete layering system that handles everything from fall hikes to midwinter ski days.
For the warmest option, go with the Icebreaker 260. For the best lightweight, the Icebreaker 175 is hard to beat. And for high-output activities, the Smartwool Intraknit solves the overheating problem that plagues standard merino midweights. Whatever your cold weather pursuit, there’s a merino wool base layer on this list built for it. Invest in quality, take care of it, and you’ll be reaching for the same base layer for years to come.