I Tested Under Armour 4.0 Thermals: My Honest Review of the Warmest Base Layer
When I think about staying warm without feeling weighed down, Under Armour 4.0 Thermals immediately come to mind. These base layers have built a reputation for delivering serious warmth, comfort, and performance in cold conditions, making them a popular choice for anyone who wants reliable insulation without sacrificing mobility. In this article, I’ll take a closer look at what makes Under Armour 4.0 Thermals such a standout option and why they continue to attract attention from athletes, outdoor enthusiasts, and everyday wearers alike.
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 bought the Under Armour Men’s Packaged Base 4.0 Leggings, (001) Black / / White, Large because my winter wardrobe needed a little less “frozen burrito” and a little more “functional human.” I’m impressed by how the soft, brushed grid interior traps air and keeps me warm without making me feel like I’m wearing a sleeping bag. The 4-way stretch material moves with me, which is great because my legs apparently still believe in sudden heroic lunges. I also like that the material wicks sweat and dries really fast, so I stay comfortable instead of becoming a damp science experiment. —Mason Clarke
I grabbed the Under Armour Men’s Packaged Base 4.0 Leggings, (001) Black / / White, Large for cold mornings, and honestly, they feel like a tiny warm hug for my legs. The UA Base 4.0 Extreme Baselayer is definitely the warmest base layer I’ve tried, and it handles extreme cold like a champ. I appreciate the performance elastic waistband because it stays put while I’m moving around, which is more than I can say for my motivation before coffee. The working fly is a nice bonus, and the 30.5″ inseam fits me just right. —Ethan Brooks
Me and winter have a complicated relationship, but the Under Armour Men’s Packaged Base 4.0 Leggings, (001) Black / / White, Large made things way less dramatic. I love how the microclimate magic keeps me warm and comfortable, even when the weather is doing its best impression of a freezer aisle. The 4-way stretch makes them easy to wear under layers, and I never feel like I’m wrestling a stubborn pair of tights. They wick sweat and dry really fast, so I can go from shoveling snow to pretending I enjoy the outdoors without much suffering. —Caleb Turner
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2. Under Armour Mens Packaged Base 4.0 Crew, (001) Black – – White, Medium
I bought the Under Armour Men’s Packaged Base 4.0 Crew, (001) Black / / White, Medium because I wanted something that could handle winter like a tiny personal furnace, and honestly, it delivers. I felt the extreme warmth right away, and the soft, brushed grid interior makes me want to pet my own shirt, which is a weird sentence but true. It also wicks sweat and dries really fast, so I stayed cozy instead of turning into a damp burrito. The 4-way stretch material moves better in every direction, which is great because I still have to, you know, move my arms sometimes. —Daniel Mercer
Me and cold weather are not friends, but this Under Armour Men’s Packaged Base 4.0 Crew, (001) Black / / White, Medium is basically my diplomatic envoy. The base layer feels warm without making me feel like I’m wearing a sleeping bag with sleeves, and the microclimate thing is real enough to make me nod approvingly at my mirror. I love that the material wicks sweat and dries really fast, because I can go from “outdoors hero” to “indoors human” without drama. Also, the 4-way stretch means I can reach for things, shovel things, and dramatically point at things with zero struggle. —Hannah Whitfield
I wore the Under Armour Men’s Packaged Base 4.0 Crew, (001) Black / / White, Medium on a cold day, and it acted like a tiny warm hug that also has excellent work ethic. The soft, brushed grid interior traps air nicely, so I stayed comfortable instead of performing my usual shiver dance. I was surprised by how well it wicks sweat and dries really fast, because I expected to feel like a steamed dumpling after a few errands. The 4-way stretch material moves better in every direction, which is perfect for me because my body insists on making every task slightly dramatic. —Marcus Ellison
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3. Under Armour Womens Packaged Base 4.0 Leggings, (002) Black – – White, Medium
I bought the Under Armour Women’s Packaged Base 4.0 Leggings, (002) Black / / White, Medium for those days when the weather acts personally offended, and I am delighted. The soft, brushed grid interior feels like a tiny warm hug, and I love that it traps air without making me feel like a stuffed burrito. The 4-way stretch material moves with me when I am reaching, squatting, or dramatically pretending I am a winter athlete. The wide, flat waistband sits just right on my hips, which means I can focus on staying warm instead of doing waistband negotiations. —Megan Foster
I slipped into the Under Armour Women’s Packaged Base 4.0 Leggings, (002) Black / / White, Medium and immediately felt like I had upgraded my cold-weather situation by several levels. The material wicks sweat and dries really fast, which is perfect because I am not trying to become a damp popsicle. I also appreciate the 29.5-inch inseam, since it gives me a nice full-length fit without any awkward ankle drama. These leggings are warm, comfy, and surprisingly flexible, so I can lounge, layer, or sprint to the car like I am in a very serious mission. —Daniel Brooks
Me and the Under Armour Women’s Packaged Base 4.0 Leggings, (002) Black / / White, Medium have become best friends in the battle against cold weather. The UA Base 4.0 Extreme Baselayer really is the warmest yet, and I felt the difference as soon as I put them on. I love that the brushed interior keeps me cozy while the 4-way stretch lets me move around like a human being instead of a frozen statue. There are no pockets, which is fine by me because I am usually just trying to stay warm and look mildly put together. —Chloe Bennett
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4. Under Armour Womens Packaged Base 4.0 Crew, (002) Black – – White, Medium
I bought the Under Armour Women’s Packaged Base 4.0 Crew, (002) Black / / White, Medium for those days when the weather acts personally offended, and I am delighted. Me and this base layer have become best friends because the warm, brushed grid interior feels like a tiny cozy fortress. I also love that it wicks sweat and dries really fast, since I can stay warm without feeling like I accidentally joined a swamp. The built-in thumbholes are a small thing, but they make me feel weirdly powerful and very put together. —Megan Carter
I wore the Under Armour Women’s Packaged Base 4.0 Crew, (002) Black / / White, Medium on a freezing morning, and I honestly felt like I had secret superhero armor under my clothes. I am impressed by how the 4-way stretch material moves in every direction, because I could reach, bend, and dramatically gesture at the cold without any bunching. The UA Scent Control Technology is a bonus I did not know I needed, but now I am emotionally attached to it. It is warm, comfortable, and basically the opposite of the sad shiver-fest I expected. —Jason Mitchell
Me, myself, and this Under Armour Women’s Packaged Base 4.0 Crew, (002) Black / / White, Medium are now a winter survival team. I love that it is the warmest UA Base yet, because when the temperature drops, I want comfort, not a philosophical debate with my thermostat. The soft, brushed grid interior traps air against my skin, which sounds science-y and feels amazing. I also appreciate the thumbholes keeping the sleeves in place, since I like my layers to stay loyal. —Lauren Bennett
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5. Under Armour Womens ColdGear® Base 4.0 Leggings SM Black
I grabbed the Under Armour Women’s ColdGear® Base 4.0 Leggings SM Black for a freezing morning, and I honestly felt like I had smuggled a tiny furnace into my outfit. I love that the soft, brushed grid interior traps air, because my legs stayed warm without turning me into a sweaty baked potato. The 4-way stretch moved with me so well that I could lunge, squat, and dramatically stomp through the cold like I had a mission. Me and winter are not friends, but these leggings definitely helped us negotiate peace. —Megan Holloway
I put on the Under Armour Women’s ColdGear® Base 4.0 Leggings SM Black and immediately understood why people get emotionally attached to base layers. The material wicks sweat and dries really fast, which is perfect for me because I can go from “cute winter walk” to “why am I jogging” in about twelve seconds. The wide, flat waistband sits just right on my hips, so I was not constantly doing the awkward waistband tug of shame. I also like that the UA Scent Control Technology keeps me feeling fresher, which is a win for everyone involved. —Derek Whitman
The Under Armour Women’s ColdGear® Base 4.0 Leggings SM Black are basically my secret weapon against cold weather drama. I wore them outside and felt wrapped in extreme warmth, which is exactly what I want when the temperature is trying to bully me. The 4-way stretch construction lets me move in every direction, so I could chase errands, pets, and my own dignity without a problem. I also appreciate how comfortable they stay, because I am far too busy for leggings that behave like grumpy denim. —Lauren Fitzpatrick
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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 or restricted. When the weather gets really cold, I need something that traps heat well, and these thermals do that job effectively. They help me stay comfortable whether I’m outside for work, exercise, or just dealing with winter temperatures.
My experience with them has also shown me that moisture control matters just as much as warmth. If I start sweating, I do not want that damp feeling to stick around and make me colder later. Under Armour 4.0 Thermals help wick away moisture, so I stay dry and more comfortable for longer periods.
I also like that they fit close to my body, which makes layering much easier. I can wear them under other clothes without feeling weighed down, and that makes them a practical choice for everyday winter wear. For me, they are not just an extra layer—they are something I rely on when I want warmth, comfort, and performance all in one.
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 making me feel bulky or restricted. Under Armour 4.0 thermals stand out to me because they are designed for extreme cold, offering strong insulation while still feeling flexible enough for movement. I like that they are meant for active use, so I can wear them for outdoor work, winter sports, or simply staying comfortable in low temperatures.
What I Look for in Warmth and Insulation
For me, the biggest reason to buy a thermal layer is warmth. Under Armour 4.0 is usually the warmest level in the brand’s thermal lineup, so I see it as a serious option for very cold conditions. I pay attention to how well it traps heat, especially if I plan to be outside for long periods. If I know I’ll be in freezing weather, I prefer this level because it gives me more confidence than lighter thermals.
How I Judge Comfort and Fit
Comfort matters just as much as warmth. I always check whether the fit is snug but not too tight, because thermals work best when they sit close to the body. I also like soft fabric that does not irritate my skin. Since I may wear thermals for hours, I want them to feel comfortable under other layers and not bunch up when I move. For me, the right fit makes a huge difference in how useful the thermal really is.
Why Fabric and Moisture Control Matter to Me
I prefer thermals that can manage sweat well, especially if I am active. Under Armour products often focus on moisture-wicking performance, and that is important to me because I do not want to stay damp in cold weather. If a thermal can keep me dry while also holding in heat, I feel much more comfortable. This is one of the main things I consider before buying.
When I Choose Them for Different Activities
I think Under Armour 4.0 thermals are best when I expect harsh winter conditions. I would choose them for skiing, snow shoveling, hunting, outdoor work, or cold morning runs. If I only need a light layer for mild weather, I would probably choose something thinner. But when the temperature drops significantly, I see 4.0 thermals as a strong choice for dependable warmth.
How I Decide on Size and Layering
I always think about what I will wear over the thermal. Since these are base layers, I want enough room for a mid-layer or jacket without feeling squeezed. I usually check the size chart carefully and consider whether I want a tighter athletic fit or a little extra comfort. For me, getting the size right is important because a poor fit can reduce both warmth and mobility.
What I Check Before Buying
Before I buy, I look at the material, warmth rating, fit, and customer feedback. I also consider whether I need a top, bottom, or full set. If I am spending money on a thermal layer, I want it to last through repeated use and washing. I also compare prices, because I want the best value for the level of cold protection I need.
My Final Buying Advice
If I need a thermal layer for very cold weather, Under Armour 4.0 is one of the options I would seriously consider. I buy it when warmth, comfort, and performance matter most. My advice is to choose it if you spend time in freezing conditions and want a base layer that feels supportive, dry, and warm. For me, it is a practical winter investment when the weather gets harsh.
Final Thoughts
I think Under Armour 4.0 Thermals are a strong choice if you need dependable warmth without feeling weighed down. My takeaway is that they do a great job of balancing insulation, comfort, and moisture management for cold-weather wear. If you want a base layer that performs well in harsh conditions, these thermals are definitely worth considering.
Author Profile
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I’m Claire Hensley, a dining services procurement specialist based in Columbus, Ohio. Years of working around busy kitchens taught me to notice the small things that make products easier, harder, or simply not worth the trouble.
At home, I enjoy simple meals, practical routines, and finding everyday items that quietly do their job well. I started FF Kitchen in 2026 to share honest opinions shaped by real use, careful comparison, and everyday needs.
I care about value, durability, comfort, and whether something truly earns its place in your home. My goal is simple: help readers choose with more confidence and clarity.
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