Kelty
Cosmic Ultra 0°F
Best lightweight sleeping bag for budget conscious winter backpackers.
Designed for demanding cold-weather expeditions, this high-performance sleeping bag balances thermal efficiency with essential comfort. The mummy-shaped design and specialized trapezoidal baffles work together to minimize heat loss, while the spacious footbox allows for natural movement throughout the night. Built with advanced hydrophobic insulation, it maintains loft and warmth even in damp, challenging conditions. An eco-friendly, water-resistant shell provides reliable protection against the elements. Thoughtful details, including a full-length draft tube, a draft collar, and an internal stash pocket, ensure you stay cozy and organized while navigating shoulder-season and winter environments in the backcountry.
$245.97
More Cosmic Options
Cosmic 20
$159.95
Cosmic Down 20
$189.95
Cosmic 40
$119.95
Cosmic Synthetic 0 Degree
$139.95
Cosmic Synthetic 20 Degree
$119.95
Cosmic Synthetic 20
$109.95
Cosmic 20 Degree Sleeping Bag
$159.95
Cosmic Ultra 20 Degree
$269.95
Cosmic
$314.95
Cosmic 20 Sleeping Bag (Long)
$109.95
Cosmic 20 Sleeping Bag
$118.22
Cosmic Ultra 0°F Sleeping Bag
$219.95
Cosmic Ultra 800 DriDown Sleeping Bag
$184.48
Cosmic 0 Synthetic Sleeping Bag
$129.95
Cosmic 20 Sleeping Bag
$118.22
Kelty Cosmic 20
$169.99
Kelty Cosmic Synthetic 0 Degree Sleeping Bag
$166.00
Kelty Cosmic Down 20
$189.95
Kelty Cosmic Ultra 0
$369.95
Cosmic Synthetic 40 Degree
$99.95
Cosmic Synthetic 20
$109.95
Owner Satisfaction
4.5
/ 5
Category Rank
842
/ 2020
#842 in Sleeping Bags
Price vs Category Average
+47%
Above average
Temperature Rating
0
/ °F
Who it's for
- Winter backpackers seeking reliable warmth without excessive pack weight
- Cold sleepers who need consistent thermal performance in freezing temperatures
- Budget-conscious adventurers wanting professional-grade gear for less money
Who should skip it
- Ultralight hikers prioritizing the smallest possible pack volume
- Side sleepers or larger individuals who require more internal wiggle room
- Campers who prioritize a completely seamless and frustration-free hardware experience
Performance breakdown
Thermal Efficiency
Trapezoidal baffles and draft collars effectively trap heat in freezing conditions.
Moisture Resistance
Hydrophobic insulation keeps you warm even when dampness creeps into camp.
Weight-to-Warmth Ratio
High-fill power down delivers serious winter insulation without excessive pack weight.
Footbox Comfort
Spacious design prevents that restrictive feeling common in technical mummy bags.
Draft Protection
Full-length tubes and collars create a reliable seal against biting winds.
Packability
Compresses well for a 0-degree bag, though it still occupies significant space.
Key Specs
Temperature Rating
0°F
Max User Height
78 inches
Weight
3.75 lbs
Insulation Type
Down
Fill Power
800 cubic inches per ounce
Shape
Mummy
Shell Material
Nylon
Lining Material
Polyester
Know before you buy
The 0°F rating represents the absolute lower limit for survival, while the ISO Comfort Rating of 18°F is the temperature at which an average sleeper will feel comfortable and warm. For most users, this bag is best suited for conditions in the high teens to low twenties.
While mummy bags are designed to be snug to trap heat, the Cosmic Ultra features a natural-fit footbox that provides extra room for your feet to move. This design balances thermal efficiency with enough space to prevent that claustrophobic feeling.
The 800-fill DriDown is treated to resist moisture, meaning it retains its loft and insulating properties much better than untreated down if it gets damp. While it is not waterproof, it is significantly more reliable in humid or misty conditions.
Yes, the bag accommodates users up to 78 inches, or 6'6", in height. You will have plenty of length, though the fit will be snugger than it would be for a shorter person.
The trapezoidal baffle construction prevents the insulation from shifting or bunching up inside the bag. By keeping the down evenly distributed, it eliminates cold spots and ensures consistent warmth throughout the night.
When compressed in its stuff sack, the bag measures 10 x 19 inches. It is a substantial piece of gear, so you should plan for it to take up a significant portion of your pack's main compartment.
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