Sea to Summit Ultralight Sleeping Bag Review (2026) — Grant's Honest Take
Our Verdict
The sleeping bag Grant actually takes on trips versus the Western Mountaineering bag he bought first.
Buy Sea to Summit Sleeping Bag on Amazon →The Bag Grant Takes vs the Bag Grant Bought
Grant owns a Western Mountaineering UltraLite rated to 20°F. It cost $700. He has used it once, on a trip where the overnight low was 38°F, which was below his expected conditions. The WM bag performed excellently. For the other trips Grant has taken, where overnight lows were 50-60°F, he takes the Sea to Summit Ultralight, which weighs 1.25 lbs and compresses to a 1-liter stuff sack.
Linda takes a Kelty bag from 2018 on the same trips. She is comfortable. Grant has noted this.
When to Use Each
The Sea to Summit Ultralight is the right bag for conditions above 45°F — summer and early fall trips at most elevations. Below that threshold, the WM bag or a warmer alternative is appropriate. Grant's error was buying the WM bag as his only bag without knowing what conditions he would actually camp in. He camps in summer. The Ultralight is sufficient for summer. He now recommends starting with a three-season bag before buying a premium cold-weather bag.
Compression and Weight
The Ultralight compresses to a 1-liter stuff sack and weighs 1.25 lbs. On the Osprey Atmos AG 65, the sleeping bag occupies the bottom compartment with significant space remaining for a sleeping pad and other gear. Grant notes this specifically because compression is the variable he underweighted when buying bags previously — a bag that does not compress well affects pack organization significantly.
Three Years of Use
Grant has used the Sea to Summit Ultralight on six trips over three years. The down fill has not compressed permanently. The zipper operates correctly. The footbox seam shows no signs of failure. At 1.25 lbs and three years of functional use, this is the highest value item in Grant's current gear inventory per dollar per year of use.
- ✓Camp primarily in summer and early fall conditions (45°F+)
- ✓Weight and pack size are primary constraints
- ✓Want a long-lasting bag from a quality brand
- ✗Camp regularly in cold weather or shoulder season below 45°F
- ✗Need a single bag for all conditions — get a 3-season or 4-season bag
- ✗Prefer synthetic fill for wet weather resilience
Pros
- 1.25 lbs weight excellent for the warmth rating
- Compresses to 1-liter stuff sack
- Three years of use with no functional degradation
- Down fill provides good warmth-to-weight ratio
Cons
- Not appropriate below 45°F — need a separate cold weather bag
- Down requires dry conditions — avoid in prolonged wet weather
- Mummy cut is snug for broad-shouldered users
Frequently Asked Questions
How It Compares
| Product | Score | Best For | |
|---|---|---|---|
| Sea to Summit Ultralight Sleeping Bag THIS REVIEW | 8.5/10 | Backpackers who camp in moderate temperatures (45°F+) and need to minimize weight | Buy Sea to Summit Sleeping Bag on Amazon |
| Osprey Atmos AG 65 | 9.1/10 | The pack this bag goes into | Buy |
| Big Agnes Copper Spur HV UL2 | 8.9/10 | The tent this bag sleeps in | Buy |
Related Reviews
Related Reading
More from Grant on this topic:
- The $3000 Sleeping Bag That Never Left the House
- Grant's First Real Backpacking Trip: The Gear Report