There is something that unites a professional geologist, an amateur fisherman and a novice hiker. What is it? Right, it’s equipment. Experienced people identify 3 basic things on the entire must-have list — the right shoes, the right backpack, and the right sleeping bag. The keyword is «right». But if you can try on shoes and a backpack, take a test drive in an urban setting, then the properties of a sleeping bag are not always obvious. Well, judge for yourself, how can a Miami resident understand whether this or that model is suitable for a vacation on the lakes in Alaska? You can get into the sleeping bag, zipper it up, try to move. But you wouldn’t know if you’d be warm outside at night. Tons of inconvenience,  ruined plans, and harm to your health will be if you don’t pay enough attention to choosing this important thing. 

Features of Kelty Cosmic Down 40

Statistically, the most popular among Americans is the Kelty Cosmic Down 40 sleeping bag. This versatile mummy-bag for the warm season. It’s considered the best in terms of price-weight-volume-temperature ratio, ideal for nature lovers and beginner travelers. The manufacturer offers us 2 modifications of  Kelty Cosmic Down 40 — Regular and Long. They’re only different in size and price. 

  Has a number of features:

  • eco-friendly 600 DriDown™ down with water-repellent DWR impregnation;
  • soft and comfortable 50D Polyester Taffeta interior fabric;
  • large, insulated hood;
  • double-sided zipper for ventilation;
  • spacious foot box;
  • zipper jam protection;
  • stash pocket for small devices. 

  Let’s compare several options to be sure of our choice.


  Perhaps this is the most important and controversial parameter. Each person perceives the temperature in his or her own way. It depends on many factors. For example, women are more sensitive to temperature comfort. Nevertheless, there is an international classification — comfort/limit/extreme.

 Kelty Cosmic 40 degree down sleeping bag review (F\ C): 

  • Extreme Rating: 15° / -9°C
  • Limit Rating: 40° / 4°C
  • Comfort Rating: 48° / 9°C

 What does it mean?

  Comfort Rating:

The bag ensures a comfortable sleep, keeping the inside at an optimum temperature of 20—22 degrees of heat at «overboard» 48 °/9 °C. 

   Limit Rating:

An adult man with an average weight of up to 80 kg will be able to spend the night outside at a temperature of 40 °/4 °C without harm to health. It’ll be less comfortable, you’ll have to put something on, but you won’t catch a cold. 

  Extreme Rating:

An adult man with an average weight of up to 80 kg will be able to spend the night in freezing temperatures down to minus 15°/ -9°C.  You will have to wear several layers of clothing. But there is no risk of frostbite.

  What do other manufacturers offer us?

For comparison: Comfort Rating of popular sleeping bags in the USA: Klymit KSB 20 20°/ -7°C, Marmot NanoWave 35  35°/ 2°C, Big Agnes Husted Sleeping Bag  30°/-1 °C.

  As you can see, choosing a sleeping bag is very important to understand the conditions in which we will use it. 


  Have you ever been on a week-long hike? Okay, let it not climbing Mount Everest, but just a Rim Trail. Have you ever noticed how much lighter your backpack gets when you take out and eat a 200-pound pack of crackers at a halt? Who doesn’t know what we’re talking about will say: What’s 200 grams? Guys, congratulations! You still have a long way to go! So, about the weight —  manufacturers struggle to reduce weight steadily.

In the Review Kelty Cosmic Down 40 says that its weight is 0.89 kg.

Information visually for comparing:

  • Marmot NanoWave 35 1.035 kg,
  • Klymit KSB 20 1.400 kg, 
  • Big Agnes Husted Sleeping Bag 1.250 kg.

 The difference is palpable, isn’t it?


  A sleeping bag is one of the most capacious things in a backpack. Official Kelty Cosmic Down 40 sleeping bag review declares 30×18 cm unpacked.

  Marmot NanoWave 35 21.59 x 30.5 cm,  Klymit KSB 20 39 cm x 20 cm,  Big Agnes Husted Sleeping Bag 22 x 25 cm, respectively.

  There is a very important point. Kelty Cosmic Down 40 compression is fantastic because it’s made from natural duck down. In other words, it will be almost three times smaller if it’s placed between two rather rigid objects. Just give it 15—20 minutes to fluff up before you go to bed. 

  Take into account in your choice your height, size and how often you move in your sleep and take a model according to your size. 


Finally, we got to the most interesting part. Of course, different sources give different prices, but still:

Kelty Cosmic Down 40 — $110

Klymit KSB 20 — $180

Marmot NanoWave 35 — $162

Big Agnes Husted Sleeping Bag — $125

Advantages and disadvantages  

 We want to point out that the kit does not include a compression bag. But it isn’t necessary: it’s easy to squeeze the bag with your hands because the filler is a duck down. This is what you need to strive for, it’s environmentally friendly, useful, comfortable, it’s in any case better than synthetic filler. By the way, if you are concerned about humanity, you can scan the QR code on the label and trace what kind of down in your particular bag. Coating with eco-friendly hydrophobic treatment and high-quality fabric to retain down is not inferior to the most expensive version. Of course, if you plan to sleep in a snowdrift, you should have winter options — bulkier, heavier. But are you going on a polar expedition so soon?

 Compare to Similar Products

 As you can see, everything is learned by comparison. We wanted to help you figure out what’s important to you. Big Agnes Husted Sleeping Bag, Marmot NanoWave 35, Klymit KSB 20 have synthetic insulation, options that are warmer, but also heavier, less compression. And, the Kelty Cosmic Down 40 is a budget summer variant for light backpacking hiking and summer camping.