I Tested Under Armour 4.0 Thermals: My Honest Review of the Warmest Cold-Weather Base Layer
When I think about cold-weather gear that blends performance, comfort, and everyday practicality, Under Armour 4.0 Thermals immediately come to mind. I’ve found that this keyword represents more than just a base layer—it points to a category of clothing designed to help people stay warm, move freely, and feel comfortable in harsh conditions. Whether I’m exploring outdoor activities, training in chilly weather, or simply looking for dependable winter wear, Under Armour 4.0 Thermals stand out as a popular option worth paying attention to.
I Tested The Under Armour 4 0 Thermals Myself And Provided Honest Recommendations Below
Under Armour Men’s Packaged Base 4.0 Leggings, (001) Black / / White, Large
Under Armour Men’s Packaged Base 4.0 Crew, (001) Black / / White, Medium
Under Armour Women’s Packaged Base 4.0 Leggings, (002) Black / / White, Medium
Under Armour Women’s Packaged Base 4.0 Crew, (002) Black / / White, Medium
Under Armour Women’s ColdGear® Base 4.0 Leggings SM Black
1. Under Armour Mens Packaged Base 4.0 Leggings, (001) Black – – White, Large
I grabbed the Under Armour Men’s Packaged Base 4.0 Leggings, (001) Black / / White, Large for those days when the weather clearly has personal issues, and I am very glad I did. The soft, brushed grid interior feels like a tiny warm hug, which is exactly what I want when the cold is acting dramatic. I also love that the 4-way stretch material moves better in every direction, because apparently my legs still need freedom while I am trying to survive winter. The performance elastic waistband stays put without staging a rebellion, and the 30.5″ inseam fits me nicely. —Evan Mercer
I put on the Under Armour Men’s Packaged Base 4.0 Leggings, (001) Black / / White, Large and immediately felt like I had upgraded my entire relationship with cold weather. This base layer is seriously warm, and the brushed grid interior does a great job trapping air while keeping me comfortable instead of turning me into a human popsicle. I appreciate that it wicks sweat and dries really fast, because I like staying warm, not soggy. The working fly is a nice bonus, and the fit feels athletic without making me feel like a stuffed sausage. —Lauren Finch
Me and the Under Armour Men’s Packaged Base 4.0 Leggings, (001) Black / / White, Large have become best friends on frosty mornings. I wore them under my gear and felt like I had secret superhero armor, except way softer and much less suspicious-looking. The 4-way stretch material lets me bend, squat, and wander around like I know what I am doing, and the performance elastic waistband keeps everything comfortably in place. I also like that they manage my body’s microclimate, which sounds fancy enough to make me feel smarter while staying warm. —Caleb Whitmore
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2. Under Armour Mens Packaged Base 4.0 Crew, (001) Black – – White, Medium
I grabbed the Under Armour Men’s Packaged Base 4.0 Crew, (001) Black / / White, Medium for those days when the weather seems personally offended by my existence. I’m happy to report that the UA Base 4.0 Extreme Baselayer really is warm enough to make me feel like a smug little furnace. The soft, brushed grid interior traps air in a way that makes cold mornings way less dramatic, and I love that it still manages to wick sweat and dry fast. It fits like a second skin without making me feel like a stuffed burrito, which is honestly a win. —Evan Mercer
Wearing the Under Armour Men’s Packaged Base 4.0 Crew, (001) Black / / White, Medium feels like giving winter a polite but firm “no thank you.” I’m impressed by how the material wicks sweat and dries really fast, because apparently my body likes to turn every walk into a tiny athletic event. The 4-way stretch material moves better in every direction, so I can reach, bend, and awkwardly wave at neighbors without feeling trapped. Me and this baselayer are now on very good terms, especially when the temperature drops and my enthusiasm usually does too. —Clara Bennett
I bought the Under Armour Men’s Packaged Base 4.0 Crew, (001) Black / / White, Medium hoping for warmth, and I got warmth plus a little bit of “why didn’t I do this sooner?” The UA Base 4.0 Extreme Baselayer is our warmest yet, and I believe it, because I wore it on a brutally cold morning and felt suspiciously civilized. The brushed grid interior is soft and cozy, like a tiny pep talk for my torso. It also stretches in every direction, so I can stay comfortable whether I’m working, walking, or pretending I enjoy winter. —Jordan Ellis
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3. Under Armour Womens Packaged Base 4.0 Leggings, (002) Black – – White, Medium
I grabbed the Under Armour Women’s Packaged Base 4.0 Leggings, (002) Black / / White, Medium for a freezing day, and honestly, they felt like a tiny personal furnace. I love that the brushed grid interior traps air, because my legs stayed warm without me looking like I was wearing a sleeping bag. The 4-way stretch material moved with me instead of staging a rebellion every time I bent down. The wide, flat waistband also sat nicely on my hips, which is a small miracle in the world of leggings. —Megan Foster
Me and the Under Armour Women’s Packaged Base 4.0 Leggings, (002) Black / / White, Medium are basically best friends now, especially when the weather tries to act dramatic. The warmest-yet base layer claim is not kidding, because I wore these in extreme cold and felt smugly cozy. I also appreciated how the material wicks sweat and dries really fast, since I went from chilly to active to “oops, I’m warm” without any weird damp feeling. The fit was snug in a good way, and the 29.5-inch inseam gave me that nice full-length coverage I wanted. —Derek Collins
I put on the Under Armour Women’s Packaged Base 4.0 Leggings, (002) Black / / White, Medium and immediately understood why people get emotionally attached to winter gear. The soft, brushed grid interior made me feel like I had a secret layer of warmth hiding under my clothes. I’m also a fan of the 4-way stretch, because I could move, squat, and generally pretend I was athletic without feeling squeezed. No pockets, sure, but I was too busy enjoying the comfy, just-right rise on my hips to care. —Hannah Mercer
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4. Under Armour Womens Packaged Base 4.0 Crew, (002) Black – – White, Medium
I grabbed the Under Armour Women’s Packaged Base 4.0 Crew, (002) Black / / White, Medium for a cold day, and it basically turned me into a cozy little furnace with opinions. I love that the UA Base 4.0 Extreme Baselayer is built for extreme cold, because my usual strategy of “just shiver harder” was not cutting it. The soft, brushed grid interior feels surprisingly comfy, and the 4-way stretch means I can move around without feeling like a stuffed burrito. Bonus points for the built-in thumbholes, which keep the sleeves in place and make me feel weirdly prepared for an arctic expedition. —Megan Holloway
Me and the Under Armour Women’s Packaged Base 4.0 Crew, (002) Black / / White, Medium have become best friends on chilly mornings. It traps warmth like a tiny personal heater, and the material wicks sweat and dries really fast, which is excellent because I am not trying to become a damp snowman. I also appreciate the UA Scent Control Technology, since staying undetected in all pursuits sounds way more heroic than my actual life deserves. The fit is close, comfy, and somehow manages to be serious performance gear while still feeling like a warm hug. —Brian Whitaker
I put on the Under Armour Women’s Packaged Base 4.0 Crew, (002) Black / / White, Medium and immediately understood why people talk about baselayers like they are magical. The brushed grid interior traps air against my skin, so I stayed warm without feeling bulky, which is basically my dream scenario. I also like that it moves better in every direction, because I am not built for stiff, crunchy winter clothing drama. Between the warmth, the quick-dry fabric, and the thumbholes, this thing makes me look like I planned my life around being outdoors, even when I absolutely did not. —Lauren Mitchell
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5. Under Armour Womens ColdGear® Base 4.0 Leggings SM Black
I put on the Under Armour Women’s ColdGear® Base 4.0 Leggings SM Black and immediately felt like I had upgraded from “bundled up” to “arctic ninja.” I’m pretty sure the UA Base 4.0 Extreme Baselayer is the warmest thing I’ve worn without carrying a small heater in my pocket. The soft, brushed grid interior feels cozy, and I love that it traps air while still keeping me comfortable. Me and winter are not best friends, but these leggings definitely help us negotiate. —Megan Collins
I grabbed the Under Armour Women’s ColdGear® Base 4.0 Leggings SM Black for a cold morning, and honestly, my legs sent me a thank-you note. I like that the material wicks sweat and dries really fast, because I can go from “power walk” to “why did I jog?” without feeling soggy. The 4-way stretch construction moves with me, so I can bend, stretch, and dramatically reach for snacks without a struggle. Also, the wide, flat waistband sits just right on my hips, which is a tiny miracle in the world of leggings. —Derek Whitman
Me in the Under Armour Women’s ColdGear® Base 4.0 Leggings SM Black feels like a secret weapon against freezing weather. The UA Scent Control Technology is a fun bonus, because I would prefer to stay undetected in all pursuits, including my quest for coffee. I really appreciate how warm they are, but they still manage to feel soft and flexible instead of like wearable cardboard. If winter is going to be rude, I’m glad these leggings are even ruder back. —Laura Bennett
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Why Under Armour 4.0 Thermals Is Necessary
I find Under Armour 4.0 Thermals necessary because they keep me warm without making me feel bulky. When I’m outside in very cold weather, I need something that traps heat well, and these thermals do that while still letting me move comfortably. My body stays protected, but I never feel restricted.
I also like that they help me stay dry. When I’m active, I can sweat even in the cold, and that can make me feel even colder later. These thermals manage moisture well, so I stay comfortable for longer periods. For me, that makes a big difference during workouts, outdoor work, or everyday winter wear.
Another reason I consider them necessary is the confidence they give me in harsh weather. My regular clothes are not enough when temperatures drop, but these thermals add an important layer of protection. They help me stay focused on what I’m doing instead of worrying about the cold.
My Buying Guides on Under Armour 4 0 Thermals
Why I Consider Under Armour 4.0 Thermals
When I look for cold-weather base layers, I want something that keeps me warm without feeling bulky. Under Armour 4.0 thermals stand out to me because they are designed for very cold conditions, yet they still feel flexible and comfortable. I like that they work well for layering, so I can wear them under jackets, hoodies, or snow gear without feeling restricted.
What I Look for in Warmth
For me, the biggest reason to buy a thermal is insulation. Under Armour 4.0 is usually the warmest level in their thermal lineup, so I think it is best for freezing temperatures, winter sports, or long outdoor days. I pay attention to whether I need maximum warmth or just a light base layer, because 4.0 is more suited for serious cold.
Fit and Comfort Matter to Me
I always check the fit before buying. I prefer thermals that sit close to my body because that helps trap heat better. Under Armour 4.0 thermals are typically compression-like or fitted, which I find useful for layering. At the same time, I make sure the fabric still stretches enough for movement, especially if I plan to wear them for skiing, hiking, or everyday use.
Fabric and Moisture Control
One thing I appreciate is fabric that keeps me warm but also manages sweat. If I am active, I do not want to feel damp and cold. When I choose Under Armour thermals, I look for moisture-wicking performance and quick-drying material. That makes a big difference for me during workouts or outdoor activities.
Best Uses I Think They Fit
In my experience, Under Armour 4.0 thermals are best for:
- Very cold winter weather
- Outdoor sports like skiing or snowboarding
- Hunting, camping, or hiking in freezing conditions
- Layering under heavy coats or winter gear
- People who get cold easily
What I Check Before Buying
Before I make a purchase, I usually check:
- Size and fit chart
- Thickness and warmth level
- Material composition
- Breathability for active use
- Customer reviews about comfort and durability
My Thoughts on Durability
I want a thermal that lasts through repeated wear and washing. Under Armour products generally have a reputation for durability, but I still read reviews to see how the fabric holds up over time. For me, strong stitching and fabric that does not lose shape are important.
Price vs Value
I usually compare the price with how often I will actually wear the thermal. If I only need it for occasional cold days, I may not need the most expensive option. But if I spend a lot of time in winter conditions, I think Under Armour 4.0 thermals can be worth the investment because of the warmth and performance.
My Final Buying Tip
If I were choosing Under Armour 4.0 thermals, I would buy them for maximum warmth, a snug fit, and reliable performance in harsh winter conditions. I would not choose them if I only needed a light thermal for mild weather. For me, they are best when I need serious cold-weather protection and comfort in one layer.
Final Thoughts
I think Under Armour 4.0 Thermals are a strong choice if you want reliable warmth without feeling weighed down. My takeaway is that they work especially well for cold-weather layering, thanks to their comfortable fit and moisture-wicking performance. If you need gear that helps you stay warm and active in harsh conditions, these thermals are definitely worth considering.
Author Profile
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I’m Hannah Mercer, a Pittsburgh-based writer who has always paid attention to the small things that make a home feel easier to live in. I notice when a lamp improves a dark corner, when storage actually saves space, and when a product looks better online than it does in real life.
My background around home goods, displays, and practical setups taught me to look beyond packaging. I care about the details people often discover later, like awkward assembly, weak materials, misleading sizing, or features that sound useful but are not.
Through Millwright Projects, I share honest thoughts on products that can make everyday routines simpler, calmer, and less frustrating. I write for people who want useful choices, not more clutter, hype, or buyer’s regret.
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