Comparison Review: Winter Down Sleeping Bags - Which one will keep you warm and sound asleep even in the freezing cold of the winter mountains?
Written by TAC
Of course, a winter sleeping bag (shraf) is an essential item when camping in a tent in the mountains in winter or spending the night in the bitter cold
Recovering your exhausted body through a warm, comfortable sleep will have a big impact on how you behave the next day. On winter mornings, it's often so comfortable inside your sleeping bag that you find it hard to get out
On the other hand, as is the case all year round in the mountains, if you spend the night without adequate bedding, you may not be able to sleep due to the cold, wake up several times during the night, and in the worst case scenario, you may even suffer from hypothermia. In that sense, although a sleeping bag is expensive, it is one piece of equipment that you need to choose carefully
So, what kind of sleeping bag should you choose? Since you'll be using it in freezing cold temperatures, it goes without saying that it needs to have good insulation. If you're camping or sleeping in a car, it's fine to just bring something warm, even if it means carrying a little extra luggage. However, that's not the case when using it for hiking or other activities. The question becomes how to achieve that warmth efficiently without sacrificing convenience or safety
As an aside, the down filling used in winter sleeping bags has specs that are comparable to those of low-quality high-end duvets, allowing you to enjoy an exquisite sleeping experience even down below
So, in order to find the one item that you can absolutely trust for winter outdoor activities, we compared and tested the winter models from three of Japan's most popular domestic manufacturers
Both sleeping bags are models that are expected to be widely used in most of Japan's 2,000m-class mountains during the harsh winter season. I couldn't help but be amazed at the craftsmanship that goes beyond just their heat retention capabilities, and is crafted with the user in mind down to the smallest details
table of contents
table of contents
- About the items tested this time
- Test Results & Spec Comparison Table
- Impressions of each model
- Detailed review of each item
- summary
About the sleeping bags we compared this time
The three models we compared this time are the three most well-known brands of sleeping bags for serious outdoor and mountain climbing. There are many excellent models overseas, but in Japan, these three companies are so dominant that they are unable to penetrate the market. This is because these brands have such high reliability in terms of basic performance
So, wouldn't you like to compare these three and see which one is better (or worse)? That's the theme of this comparison test!
There are many different models of winter sleeping bags depending on the quality and amount of down, but for this particular environment, we chose a lightweight model suitable for mountain climbing, with a maximum operating temperature of around -10°C, to ensure it would be suitable for mid-level mountains (2,000m above sea level south of Tohoku) in the harsh winter
- ISUKA AIR 630EX
- Mont-Bell Alpine Down Hugger 800 #1
- NANGA UDD BAG 630DX
Test environment
The test period spanned two seasons, from 2018 to 2019, during Hokkaido's harsh winter. The test was conducted while camping in a tent, in a car, and outdoors in strong winds. The sleeping arrangement consisted of a base layer, fleece, and down jacket for the upper body, and a base layer and trekking pants for the lower body
I also tried to sleep in a sleeping bag at home to test its comfort. In total, I ended up sleeping in a sleeping bag for about two months!
The following five points were set as indicators for the evaluation items and the review was conducted
- Heat retention...Needless to say, the most important factor in a winter sleeping bag. Of course, just because it's warm doesn't mean it doesn't matter how heavy it is. Also, this is only a comparison between the models we've looked at here, so it doesn't apply to all models from the same brand
- Weight: Winter mountain gear is bulky, so you want to keep the weight as low as possible. However, the balance with heat retention is also important, so simply being light is not enough
- Comfort: Check how comfortable it is to sleep on. It can be frustrating if the mattress is too cramped in an effort to balance weight and warmth
- Portability (storage capacity): As with the weight mentioned above, this is an important point to consider when carrying the device
- Functionality and water repellency: We check how well the product meets the actual usage scenarios of users, including ease of use and ability to withstand adverse conditions
Test Results & Spec Comparison Table
If you find it difficult to see the table on the lightweight display for smartphones, click here.
| comprehensive evaluation | AAA | AAA | AA |
|---|---|---|---|
| item |  ISUKA AIR 630EX |  Mont-Bell Alpine Down Hugger 800 #1 |  NANGA UDD BAG 630DX |
| Reference price | 51,840 yen | 37,800 yen | 51,840 yen |
| Here is ◎ |
|
|
|
| Here is △ |
|
|
|
| Heat retention | ★★★★★ | ★★★★☆ | ★★★☆☆ |
| weight | ★★★☆☆ | ★★★★★ | ★★★★☆ |
| Comfort | ★★★★★ | ★★★★☆ | ★★★★☆ |
| Portability | ★★★☆☆ | ★★★★☆ | ★★★★☆ |
| Functionality | ★★★★☆ | ★★★☆☆ | ★★★★★ |
| Specifications | |||
| item | ISUKA AIR 630EX | Mont-Bell Alpine Down Hugger 800 #1 | NANGA UDD BAG 630DX |
| Manufacturer's specified temperature range (℃) |
*ISUKA's own standards |
*EN13537 |
*EN13537 |
| Size (cm) | 80 (shoulder width) x 213 (total length) cm | Up to 183cm | Maximum length: 210 x maximum shoulder width 80/cm (up to 178cm tall) |
| Actual weight (including storage bag) | 1150g | 924g | Approximately 1,080g |
| Storage size (cm) | φ20×34cm | φ17×34cm（6.2L） | φ17 × 31cm Accessories: Shoulder warmer included |
| material | 100% nylon (nylon 66) | Outer: 10-denier Ballistic® Airlite [Polkatex® processing] | 15dn nylon sheer water repellent finish |
| Down quality | 800 fill power white goose down (90/10) | 800 fill power EX down | 770 fill power European duck down (90/10) with ultra-water-repellent finish |
| Down amount | 630g | not clear | 630g |
| Zipper specifications | YKK anti-snap zipper | R (right) zipper | YKK anti-snag zipper |
Impressions of each model
ISUKA AIR 630EX
Here is ◎
- Excellent heat retention
- touch
- Fit
- The zipper is very smooth
Here is △
- Shallow hood
- Storage size and weight
The shoulder warmers wrap around the front and back of the neck and fit naturally without the need for adjustment
In one word, it can be described as "simple and sturdy." It is a model that focuses on one thing: a comfortable sleep, and is packed with high heat retention and simple functions, making it safe to use even in the harshest winters
The soft inner fabric and the highly resilient 800FP white goose down filling not only allowed me to sleep soundly until morning even during field tests at -15°C, but also provided an exceptional sleeping comfort that rivals that of a luxury down comforter
In my opinion, this model has the best heat retention of the three. In particular, the extra down in the foot area kept my feet warm until the morning. This made me think that the manufacturer's specification of "minimum operating temperature -15°C" is probably close to the "limit temperature" defined by the EN standard
Unlike the other two models, the U-shaped shoulder warmer that wraps around the neck is not tightened with a drawstring, but the soft fabric fits well, so it doesn't bother me. In fact, I personally prefer it without a drawstring, as it's simpler and doesn't get in the way
In addition, the draft tubes located in the zipper area effectively prevent cold air from getting in. The zipper, which is designed to reduce snagging, generally works well, but it did sometimes snag, so I feel there is still room for improvement
In the waterproof test, the outer fabric was water-repellent, and even after showering for about three minutes, the water did not penetrate the down. However, once the down got wet, it became soggy, making it difficult to use in the field
The hood is the shallowest of the three models and does not completely cover the entire head, so when used outdoors in strong winds, it was inevitable that my head and face would get cold
Although it is the most expensive sleeping bag on this list, I think that the warmth, comfort, and functionality it offers are well worth the price. It's a product of ISUKA, a brand Japan is proud of. This is a model that I can confidently recommend
Mont-Bell Alpine Down Hugger 800 #1
Here is ◎
- Stretchability
- Storage capacity
- light
- Water-repellent outer surface
Here is △
- Neck fit
- Zipper jamming
Montbell is the only brand that has double draft tubes to prevent cold air from coming through the zipper
As it is the cheapest of the three models, I honestly underestimated it at first, but in conclusion, my expectations were exceeded in a good way. It is truly a high-cost performance product
The first thing that surprised me was the high level of insulation. Filled with 800FP EX down, which boasts high resilience, the sleeping bag felt a little warmer than the NANGA, which has the same temperature rating, although it wasn't as warm as the ISUKA. This subtle difference doesn't seem to be due to the quality of the down, but rather to the various mechanisms that prevent cold air from entering, such as the densely woven outer fabric "Ballistic Airlite," the neck baffle around the neck, and the "Double Draft Tube" attached to both sides of the zipper
And best of all, Montbell's unique "Spiral Stretch System" allows even me, a quirky sleeper, to move around comfortably inside the sleeping bag, providing unparalleled comfort. I was able to easily change clothes inside the sleeping bag, and since it allows me to sit cross-legged, I can wear it even when I'm not sleeping during the coldest of months. It's also warm and extremely convenient
The included stuff sack also uses the same spiral stretch system as the sleeping bag, which not only reduces stress when storing it, but also allows it to change shape to fit into dead space inside the backpack, making packing much easier
Unfortunately, the zipper got stuck quite often. It happened about once in three tries, especially when closing the zipper from the inside while inside the sleeping bag. Even then, forcing it closed could damage the fabric, so the more careful I was, the longer it took, which was very stressful
Overall, it is lightweight, has excellent cost performance, and offers unparalleled comfort with features such as stretchability, but I feel that it falls short of the other two in terms of comfort and the craftsmanship of the small parts
NANGA UDD BAG 630DX
Here is ◎
- touch
- Large hood
- Water-repellent down
- Smooth zipper that is hard to pinch
- Storage size
Here is △
- Heat retention
- Cold air from the zipper
The most comfortable zipper I found this time was NANGA's anti-snag zipper
Speaking of NANGA, they offer a very welcome "lifetime warranty." This system makes users want to treasure their products for the rest of their lives. NANGA has released the UDD BAG 630DX, which is made from DX down, made from European white duck down washed domestically. This DX down has been given an ultra-water-repellent finish, resulting in a water-resistant down that "allows moisture to pass through but does not absorb water," making it the UDD
While water resistance is a concern, let's start with the warmth. The insulation was more than satisfactory within the specified temperature range (up to -10°C). The neck and draft tubes are well-designed to prevent cold air from entering, and the large hood keeps the head warm, making it an excellent design. However, when compared in more severe environments, such as temperatures exceeding the limit, around -15°C, or in strong winds, this jacket was the most susceptible to cold. I felt the cold particularly strongly through the zipper and my feet. While this may be due to differences in down quality, I was surprised that it felt colder than the Montbell jacket, which meets the same EN standards
Now, as for its water resistance, when we submerged the down in water, it immediately floated up. Even after repeated submersion, the result was the same: the down got a little wet, but it didn't become soggy. This result was surprising, as the other two models not only didn't float up after repeated submersion, but they also became soggy. Of course, down that gets wet loses its heat-retaining properties, but UDD, which repels some moisture and water, is less likely to lose its heat-retaining properties even when used for long periods in harsh environments
The zipper is luminous and designed to reduce snagging. It's very easy to see even in the dark, which is very helpful. The snagging reduction feature also works well. In reality, if you close the zipper too quickly without stretching the fabric, it will still get caught to a certain extent
Although it is slightly less warm than the other three models, it has unique appeal, such as the ease of use and security of the water-repellent down, the fine details including the luminous zipper, and the reliability of the lifetime warranty system