Brrrrrrrrr! It's freezing! I wish I had a super-warm, comfortable shirt that wasn't bulky to keep me nice and toasty in winter... mybest is here to help!
Our editors searched Japanese e-commerce sites such as Amazon, Rakuten, and Kakaku.com for the best warm innerwear shirts available online. We then picked out the most popular products and tested them.
In our evaluation, we focused on 3 things:
We then ranked the products and put what we learned into a buying guide to help you choose the best Japanese warm inners available online.
We picked out some of the most popular products and tested them for heat generation, comfort, and design.
Then, based on our tests, we ranked the top 13 Japanese warm inner shirts available online.
Japanese prices for some of the products are given, but they've been converted into US dollars to make it easy for you.
|Japanese||GUNZEインナーシャツ ホットマジック 極-kiwami- 8分袖|
|Materials||55% acrylic, 20% synthetic fiber (acrylate fiber), 20% nylon, 5% polyurethane|
|Heat Generation||A+ (+7.2℉)|
|Japanese||イトーヨーカドーセブンプレミアムライフスタイル ボディヒーター 婦人 厚地長袖シャツ|
|Materials||33% acrylic, 31% rayon, 18% nylon, 17% cotton, 1% polyurethane|
|Heat Generation||A+ (+6.8℉)|
|Materials||46% rayon, 30% acrylic, 19% polyester, 5% polyurethane|
|Heat Generation||A (+5℉)|
|Materials||Cotton 90%, Wool 10%|
|Heat Generation||A+ (7.2℉)|
|Japanese||ワコールスゴ衣 天然素材プラス やわらか、ひびきにくい ニットトップ スタンダードUネック|
|Materials||90% cotton, 10% polyurethane|
|Heat Generation||B (3.8℉)|
Inner Shirt Hot Magic
Seven Premium Lifestyle Body Heater
Heattech Extra Warm
Cotton and Wool Warm Midwinter
Amazing Clothing Natural Material Plus Knit Top
|Features||mybest's Top Choice! Comfor...||Perfectly Warm, Thick, and ...||Recommended for Moderate an...||Recommended if You Want Nat...||So Thin, You Can Wear it Li...|
|Japanese||GUNZEインナーシャツ ホットマジック 極-kiwami- 8分袖||イトーヨーカドーセブンプレミアムライフスタイル ボディヒーター 婦人 厚地長袖シャツ||ユニクロヒートテックエクストラウォームUネックT（8分袖・極暖）||無印良品綿とウールで真冬もあったかＵネック八分袖Ｔシャツ||ワコールスゴ衣 天然素材プラス やわらか、ひびきにくい ニットトップ スタンダードUネック|
|Materials||55% acrylic, 20% synthetic fiber (acrylate fiber), 20% nylon, 5% polyurethane||33% acrylic, 31% rayon, 18% nylon, 17% cotton, 1% polyurethane||46% rayon, 30% acrylic, 19% polyester, 5% polyurethane||Cotton 90%, Wool 10%||90% cotton, 10% polyurethane|
|Heat Generation||A+ (+7.2℉)||A+ (+6.8℉)||A (+5℉)||A+ (7.2℉)||B (3.8℉)|
And why they didn't quite make it.
It's Hottie Furry by PeachJohn has sweat absorption pads in the armpits to prevent stains and wetness from showing. But they're kind of stiff and irritating. The wide collar is good for being invisible under other tops, but bad for showing bra straps. It's moderately warm.
Wacoal's Amazing Clothing Comfort Plus is a really stylish design, with a lace front collar that we want to show off by letting it peek out from under our blouse. Unfortunately, it didn't generate heat at all, so we'd call it just a regular undershirt. But it's smooth and soft.
Uniqlo's regular Heattech line is probably the most well-known heat generating inner, but it actually didn't prove it was worthy of top-tier status. The thin fabric and open neck mean it lets cool air in. However, it fits well, and the material feels nice on the skin.
Innershirt KireiLabo by Gunze is thick, with a fleece back and small neck opening. So in that sense, it was warm. But we found that the heat generating properties were very low.
Shimamura's Thick-Lined Warm Inner is stretchy and comfortable. The brushed fleece material is warm, but it doesn't generate heat so well. It would be good for wearing under a sweater.
The other product we tested from Shimamura, the Brushed-Fleece Back Inner, is tight like a wetsuit and holds your body temperature to protect from cold. However, it doesn't produce much heat, so if you sweat it may chill you. The wide neckline may not hide your bra straps.
Breath Thermo Every Plus from Mizuno was uncomfortable, not particularly warm, and expensive because of the exclusive technology used to produce it. But most of all, the color, fit, and design combined to make us look frumpy.
We put each product through 3 tests. The products were then given grades from A+ to D.
Heating fabrics work by producing heat from the absorption of moisture. (This exothermic process is called hygroscopic heat generation, if you're interested in the science!) To test this functionality, we enlisted the help of a specialized institution to measure the level of moisture absorption and exothermicity of the fabric of each product.
The fabric was placed in an environment where the humidity increased over time, and then the change in surface temperature was checked every 60 seconds. Fabric that had a larger temperature difference is better at moisture absorption and heat generation.
Our tests showed that both synthetic materials AND natural materials can generate heat well. The highest-performing shirts were one with a 20% acrylate fiber blend, and another with a cotton/wool blend.
Our testers wore the shirts and rated them for how they felt and whether or not they were warm. We looked for fabrics that were not stiff or itchy. We also gave lower rating to ones that were too thin or felt cool to the touch. Our results showed that brushed, fleecy inners were the warmest and most comfortable.
This type of material feels warm as soon as you put it on. It's soft, too. We didn't notice a consistent difference in comfort between natural and synthetic fabrics; some of the natural materials felt itchy, and some of the synthetics were uncomfortable.
We checked the size and cut of the collar, the sleeve length, and the color and texture of the fabric. We also looked at how the seams were sewn. The highest scores went to products that look nice enough to wear as outer shirts, or showing partially under another shirt like an unbuttoned flannel.
We gave low marks to shirts that were so thin they were see-through. We also were unimpressed with necklines that left our bra straps exposed. Heavier weight fabrics and deep V-necks scored better.
We have a few tips to help you choose the best warm innerwear.
When you sweat, your body cools down. If you sweat in a cold environment, your body could lose heat rapidly. But if you are wearing hygroscopic exothermic fabric, sweating will generate heat and you'll stay warm. And if you move from a warm room to the cold outdoors, a good shirt should keep your body at the same stable temperature.
Natural material like cotton, wool, and silk are highly hygroscopic. Wool is particularly good, but many people don't like the itchiness. So, wool is often blended with cotton for undergarments.
Synthetic fibers are generally less hygroscopic than natural fabrics. To improve their functionality, they are often blended with acrylate fibers, so look for that term on the label.
Even if you plan to use it only as an undershirt, there may be times when it shows. What if it peeks out from your sleeve during a job interview, and it looks like grandma pajamas?!
Even if you're not so fashion-conscious, a nice design can be worn as a shirt by itself, so it's more versatile. Consider the neckline, sleeves, hems, seams, color and texture.
To keep your body warm from the inside, try to:
You'll need a lot more than good innerwear to stay comfortable during the cold winter months. Here are some other great products to help you survive!
mybest looked at 13 of the most popular Japanese warm inners available online and tested them all. We found that natural fabrics felt like quality items, but synthetics absorbed moisture better, generated heat efficiently, and were generally warmer.
Writing: Sayako Suzuki/Translation: Susan Lucier-Ogawa/Photos: Koichi Miura
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