There's no getting around it: this bag comes in at the bottom of the heap in nearly every one of our testing metrics. If the high price of premium down feathers is stopping you from enjoying cold weather camping, the Cosmic Down will keep you warm, but for a little more dough you can pick up the Rab Ascent 900, a bag that is appropriately light enough and more technically qualified for backpacking.
The Cosmic Down gets its loft from 33oz of 600 fill power down.
With 33oz of 600 fill power duck down, the Cosmic Down earns a 6, putting it as warm as the super light Western Mountaineering Versalite, which costs $320 more and is almost two pounds lighter. The Cosmic Down beats the Nemo Sonic in warmth, but is much heavier, and less weather resistant. A draft collar and an effective draft tube help trap in heat and so does the narrow foot box.
While not as comfortable for tossing and turning or stomach sleeping, a narrow cut reduces the uninsulated space in the bag, keeping the user warmer. While this bag's shell fabric compromises weather resistance, and low fill power down adversely affects packability, warmth is one metric where this budget-friendly bag still excels.
At 4 lbs 1.5oz, the Cosmic 0 is the heaviest bag in our review, just .2oz heavier than one the warmest bags in the review, the Marmot Col. This is because of the relatively heavy shell materials and the 33oz of duck down needed to achieve the same warmth as lighter bags with higher quality down like the Western Mountaineering Versalite.
While thick and durable, the 50 denier ripstop shell adds lots of weight. The fill weight to material weight ratio on this bag is about 1:1, where on the Versalite, it's 3:1. This bag has a relatively poor warmth to weight ratio, and wouldn't be our first choice to lug into the mountains, but it's still lighter than many of the synthetic options out there. If you aren't hiking far, this Best Buy on a Tight Budget could be the ticket, especially if you're looking to save some Benjamins.
The draft tube does a good job of keeping out the cold air, but tends to get snagged in the zipper.
A generous 62" of girth around the shoulders make it possible for back and side sleepers to snuggle in comfortably. The foot box is on the narrow side at 40", which helps maintain heat efficiently, but doesn't allow for much space to spread your feet around compared to the Rab Ascent 900 (49"), or the luxurious Nemo Sonic 0 (53").
Overall, this bag is roomier than lighter bags like the Western Mountaineering Antelope MF, the Feathered Friends Snowbunting, and the Western Mountaineering Versalite, but these bags trade space for thermal efficiency. We feel that staying warm in bitter cold winter conditions affects our comfort level more than room to spread out. If you think you'll be spending hundreds of hours inside a sleeping bag this winter, you'll want something more spacious like the Rab Ascent 900 or the Big Agnes Storm King.
With a good compression sack and a little muscle, this bag will fit the average backpack.
The 600 fill down is the least compressible fill material in our selection, but the Cosmic 0 packs down smaller than the Marmot Col and The North Face Inferno -20, both of which contain more down and have roomier cuts.
The Western Mountaineering Versalite packs down to about half the size of the Cosmic. The included stuff sack is huge, but our testers managed to cram it down to a backpackable size with a compression sack. If you're primarily looking for a sleeping bag for car camping or short backpacking trips, packed size is less of a concern.
Though inexpensive, this bag still has a decent draft collar and draft tube, two essential features for keeping you warm.
The Cosmic 0 offers many features similar to bags two and three times its price. It has a full-length draft tube that hangs down over the zipper and keeps out wind and moisture. When fully zipped, the draft collar rests under the chin, but it doesn't have its own cinch cord. The hood is a bit shallow compared to the Nemo Sonic or the Big Agnes Storm King 0, but is well insulated and kept our testers' heads toasty.
We feel that deeper hoods are generally more comfortable, as they aren't as claustrophobic feeling and it's easier to completely cover our faces when it's super cold out. The Cosmic 0 has four webbing loops to tie cord to and fasten to a sleeping pad. Like the pad sleeve on the Big Agnes Storm King 0, our testers had various opinions on this feature.
Oops. Be careful not to get the sleeping pad tie-on points stuck in the zipper.
Some thought that the tie-in points were helpful for staying on the pad all night, others felt they were unnecessary and inhibited them from sitting up in the bag to drink coffee or investigate curious nighttime sounds. Our lead tester accidentally got one of the loops caught in the zipper and almost ripped it off. Overall, we felt that this bag has one of the more "snaggy" zippers in our review selection. The Cosmic does not have a stash pocket, but a small stuff sack will do the trick if you need to keep small items like batteries warm inside the bag.
The Kelty Cosmic Down was the only bag to wet through in our rain testing due to its sewn through construction.
This bag scored low in this metric because it wetted out through the stitching in our light rain test, and it was the only bag in our review that had this problem. It also absorbed the most water in our submersion test and took the longest to dry. The good news is that you probably won't be using your 0-degree bag in a rainstorm and weather resistance is the least of your concerns if your sleeping bag is submerged under water.
Nonetheless, these tests illustrate that the Cosmic is more vulnerable to melting snow and condensation than the other bags. This problem can be alleviated by a good backpacking tent or bivy sack. The Rab Ascent 900 performed much better against the elements and snagged our Best Bang For Your Buck Award.
Though water was able to soak through at the seams, the shell fabric still sheds water.
4 lbs is heavy to be lugging around in the backcountry, and the Cosmic doesn't have a good warmth-to-weight ratio, however, this bag packs down small enough that it would be worth taking on shorter trips. In car camping situations where weight isn't an issue and you are sleeping in a waterproof tent or vehicle, the Cosmic is a great choice for folks on a budget.
At $220, the Cosmic 0 will keep you warm in the low temps for a low price. However, the Rab Ascent 900 is lighter, more weather resistant, and just as warm for a relatively low price of $349.95, so it receives our Best Bang For Your Buck Award.
If you're on a budget and don't want to miss out on some winter adventures because you don't have a warm bag, check out the Kelty Cosmic Down 0, just make sure you have a good tent or bivy sack if precipitation is in the forecast. For a few short trips a year, the price can't be beat. Though heavy, this bag is plenty warm for sleeping temps down to the single digits, and lack of weather resistance is the only glaring concern here. For about $100 you can grab a lighter, more weather resistant bag like the Big Agnes Storm King 0 or the Rab Ascent 900.