Kelty Cosmic Synthetic Fill 0 Degree Backpacking Sleeping Bag - Lightweight, Water-Resistant for Winter Camping & Hiking - Includes Compression Straps & Stuff Sack - Perfect for Cold Weather Adventures, Backpacking Trips & Outdoor Survival

Yes, yes, yes! Finally found a really warm sleeping bag!1. The first thing to know about sleeping bags is cotton vs. synthetic vs. down. Cotton is dirt cheap, but very heavy, and not effective when wet. They should only be used at the campsite. Down is the most expensive, packs down small, is very light, but hard to clean, can irritate allergies, aren’t vegan (if that matters to you), and not effective when wet. Synthetic bags are the best compromise, as their cost is in the middle, they are still effective when wet, and not too heavy. This is a synthetic bag.2. The second thing to know about sleeping bags is that the number in the title means little. What you want to know is the actual comfort temperature. For the Kelty Cosmic Synthetic 0, per their website, it’s 18 degrees. This is excellent, as for many zero degree sleeping bags, you will survive at zero degrees, but you won’t be comfortable unless the temperature is in the thirties or higher.3. The third thing to know about sleeping bags is there is an ISO 23537 (previously EN 13537) standardized test that will verify the true capability of the sleeping bag, instead of relying on guesses from the manufacturer. Kelty has had this sleeping bag tested to come up with that 18 degree comfort temperature.4. The fourth thing to know about sleeping bags is those ISO/EN tests are assuming that a) you are wearing long underwear and socks, and b) you are on an INSULATED pad that is rated at R-4.8 or higher (the same rating measurement standard as the insulation in your house). Otherwise, the cold ground will just suck the heat off of you. My pad is rated at R-4.5, so in the ballpark.5. I have only tested this bag at 40 degrees so far, but it’s much warmer than my other “zero” degree sleeping bags. I took my balaclava off for the whole night and didn’t cinch the bag around my face. I’ve never done that before with my other bags at that temperature. The baffles around the neck and zipper work well.6. A big factor in its effectiveness is it does a really good job puffing up, as air is the primary insulator in sleeping bags. It really fights me when I’m trying to get it back in its stuff sack. That’s a good thing. When I’m storing it in a black garbage bag (recommended for long term storage, or hanging them vertically), it easily fills the whole bag.7. This will fit in a 55 liter backpack when in the stuff sack, but just barely, and will take up half of the available space. I also have to put it in vertically, and just push it down once it’s in. You can also not use the stuff sack and just shove it down there inside a compactor bag. Any synthetic sleeping bag takes up substantial space, but this takes up more space than my other sleeping bags.8. I got the long version, and weighed it at 4.95 pounds, just about right on the mark of the advertised weight of 5.0 pounds, and that includes the 4-ounce stuff sack. I’ve had bags be substantially lighter, which makes me question their quality control.9. The stuff sack feels flimsier than other stuff sacks, but it is also a few ounces lighter than my other stuff sacks. It comes with a cap, which doesn’t make the sack waterproof, but definitely more water resistant, as my other stuff sacks just have a flap at most to try to cover the hole that isn’t very effective.10. There are straps sewn along the zipper to keep it catching on the bag. The zipper works well until it gets up to my bicep, and then I have trouble zipping it the rest of the way. It’s an art to try to get it to zip the rest of the way, which involves two hands. This is the only negative I can think about this bag. It doesn’t have Velcro to keep the zipper from coming undone. It was unzipped a few inches when I woke up. I was warm, so maybe I pulled the opening up a little bit to cool off, I dunno.11. The zipper stops just a few feet from the bottom of the bag. I don’t know why the manufacturer’s pictures show it only unzipped at the elbow. You can use the bag as a blanket, with a little foot hole, like most other mummy bags.12. I’m 5’11” and 200 pounds, and I was comfortable in this long version, with adequate footspace. My arms were able to rest alongside my body with no issues. I was able to turn without having to take the bag with me.13. There is a small zippered pocket near your head that can barely hold an iPhone 7, but I just use it for a headlamp. I like that it’s zippered, because I’ve had items fall out of Velcroed pockets. You should stash your electronics (phone, headlamp, GPS, pad inflator, battery backup, etc.) in your bag because cold weather will zap the charge, so you can throw the rest in your footwell. Stash your water filter, too, because if it freezes with water particles in it, it will be ruined.14. If you want to save weight with the same comfort temperature rating, you can get their down Cosmic Ultra 0 and save ten ounces for an additional $240. So yeah, this is a good deal.15. Overall, this is a heavy sleeping bag, so it’s best as a winter-only bag, but I was so impressed with it, I ordered their 40-degree synthetic bag the next day, which has a comfort temperature of 37 degrees, but weighs only 2.36 pounds for the standard length. However, the standard size ended up being too restricting for me width-wise, so I'm glad I got the long version for this.