What to Look for in a Winter Sleeping Bag Part 2

This is part 2 of the unbiased winter sleeping bag guide. Now, let’s talk about form, cuin, fill wight, ratios and temp ratings. Part 1 can be found here.

Winter Sleeping Bag:

Form factor

The next decision is the form of the sleeping bag. The most common forms are the mummy and rectangular. Whereas the former generally is tighter and fits the shape of a body better, the latter allows for a more comfortable bed-like experience. Keep in mind that you would like to have a winter sleeping bag that is not too loose around your body due to warmth issues, but at the same time has enough space for some clothing to keep them warm to wear them in the morning.

Form Features

Further consideration should be given to the draft collar, hood and draft tube. All of these prevent the cold entering the sleeping bag. The hood depends on personal preference whether to sleep on one’s back or on the side. Some sleeping bags have more down in the hood to function as a pillow, which I think is unnecessary because it will be compressed. If sleeping side ways is preferred, a larger hood might increase comfort. The draft tube (covering the zipper) and collar (tightening around the face) should be filled properly. This avoids cold spots.

Pockets are nice to have, as long as they are inside the sleeping bag. Otherwise batteries might still be damaged due to the cold. However, even without any pockets inside the sleeping bag you should take them inside and store next to your body.

Cold environments pose a challenge for the right equipment winter sleeping bag switzerland outdoor
Cold environments pose a challenge for the right equipment

What’s your weak point?

Another crucial form factor, is a foot box with added insulation. I am used to floor heating. Given that my feet never really have to worry about warmth at home, they are not very well accustomed to the cold. Hence, an increased amount of down around the feet is highly appreciated. Additional warmth cane be achieved by using dry bed socks or even down socks.

It is crucial that the form of the sleeping bag suits your body form. If it is too tight, the down will not achieve its full loft. Hence, the insulation is impaired from the true potential. At the same time, too much space will be hard to warm up with your body heat. Make sure you test the sleeping bag in store. If you plan on using it with your summer sleeping bag, take it with you as well.


Cuin is a combination of cubic and inch and shows the loftiness of 1 ounce of down (=28,3495 grams). The capability to dramatically increase in volume is the key to the unmatched insulation value per weight of down. The number of Cuin ranges from 300 to 900. This number equals the quality of down. The larger the number the more qualitative down is in the sleeping bag. This higher the quality of down, the less you need to achieve the same insulation power as with lower quality. Thus, the sleeping bag becomes lighter and can be packed smaller. Keep in mind that what in the US is declared as 900 fill is in the EU only 850+ due to stricter regulations in the test environment!

fire and snow

Fill Weight

This is the amount of down that is in the sleeping bag [in grams or ounces]. Some brands to not overtly state this number on their sleeping bags, but a quick only research reveals it. According to Wikipedia, a sleeping bag using 550 fill power down, for instance, would have to use approximately 40-50% more fill of down than a similar item that uses 800 fill power down to provide the same loft.

When subtracting the fill weight number from the total weight, you get the weight of the fabric and additional accessories. The smaller this number, the lighter the fabric and more prone to tearing. However, I would rather have an ultralight sleeping bag and protect it with a bivy because a sleeping bag will never be as waterproof as a real outer shell designed to withstand the environment.

Down/Feather Ratio

Oftentimes, there is a ratio added which reads, for example, 90/10 or 80/20. This ratio shows how much of the material is true down and feathers. You might wonder what the difference is: Down is the fluffy undergrowth between the feathers and is much better in insulating. So, the higher the first number, the more down is in the sleeping bag. Usually, when looking at 800+ Cuin the ratio reads between 90 to 95 percent down.

Temperature rating

The temperature rating is down (position) here for a reason. This is probably the most misused number in the sleeping bag industry. Even though it seems to be normed according the EU or US regulations measured with a plastic model in a controlled environment, it does not do justice to a true temperature rating.

First, it uses an outdated sleeping pad with a low R-value. Hence, it does not adequately represent temperature ratings for sleeping bags which have more down on top than on the compressed back.

Secondly, it gives three numbers (comfort, limit and risk) of which none really is representative. Comfort should be at what temperature you sleep well, limit is where you possibly need to move to stay warm and risk should be when there is considerable harm to your body. The reason that these ratings are inaccurate are the personal thermal sensitivity, the body shape, and other circumstances, which cannot be standardized.

The temperature rating should be taken with a grain of salt.

Thus, it is very risky to rely on temperature ratings, unless you have experience with sleeping bags of certain brands. It might be a good idea to try a sleeping bag of a friend to find out about the true temperature rating. The temperature rating should be taken with a grain of salt.

Trying the sleeping bags in store
Trying the sleeping bags in store


Choosing a sleeping bag is not an easy decision. There is not the best winter sleeping bag out there. The choice highly depends on your activities and needs. Backpackers are most concerned about weight and pack size. Car campers will have a different priority. I hope this unbiased sleeping bag guide has helped you to understand the industry and its technical terms a little better.

The most crucial factors for me are clearly the form, cuin, and fill weight. First, I need a bag, which can run to its full potential by fitting snuggly but has enough space for some clothes or combining with my summer sleeping bag. Secondly, the quality of the down allows a small pack size because I have to carry the bag. Thirdly, I look for the largest amount of goose down that my budget can buy.

Here’s a report where I slept outdoor to photograph the Geminid meteor shower check it out!

Let me know in the comment section below which winter sleeping bag is your choice.

Winter Sleeping Bag:

Chilly morning in the Canadian backcountry: no problem with the right winter sleeping bag
Chilly morning in the Canadian backcountry: no problem with the right winter sleeping bag

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