Sea to Summit Trek Down
Rating
Versatility: 5
Size/Weight: 7
Features: 6
Construction: 8
Sleep Quality: 7
OVERALL: 6.6
Our top pick for spacious, adaptable comfort.
The Sea to Summit Trek Down is a semi-rectangular sleeping bag that blends the warmth of a mummy bag with the roominess of a traditional design. Its 650+ fill power RDS-certified down delivers reliable insulation, while the Free-Flow zipper system allows for customizable ventilation, making it perfect for campers who want to adjust their warmth on the fly. We love the thoughtful extras, like the dual storage sacks and the ability to zip two bags together for couples.
Best For: Car camping, overlanding and casual backpacking
Pros: Roomy yet warm, versatile zipper system, ethically sourced materials
Cons: Not the most compact, can feel clammy in humid conditions
Verdict: A top-tier choice for campers who prioritize comfort and flexibility over ultralight packing
Skip ahead to First Impressions, Sleeping Experience, Features Analysis, Construction and Durability, or the Final Verdict, or check out how Sea to Summit Trek Down compares to others in our list of the Top 5 Sleeping Bags.
Specs:
Packed Size: N/A
Weight: 3lbs 2.7oz
Fill: 650-Fill Duck Down
Approx Price: $399.00
First Impressions
Right out of the stuff sack, the Sea to Summit Trek Down makes a strong impression with its plush, high-loft 650+ fill power down and thoughtful design touches. The semi-rectangular shape immediately stands out as a smart middle ground, as it’s roomier than a mummy bag but more thermally efficient than a basic rectangle. The included compression and storage sacks are nice bonuses, though some users note it doesn’t pack down as small as ultralight backpackers might hope. The Free-Flow zipper system looks innovative, but a few reviewers found it overly complex compared to traditional designs.
Sleeping Experience
This bag shines in cold weather, keeping you warm very close to its 15°F weather rating (you may be able to even push it into single digits with a liner). The spacious cut is a hit with side sleepers and restless campers who hate feeling confined. The ability to unzip the footbox or fully open the bag like a quilt adds versatility for warmer nights, however, you may notice some breathability issues in milder temps (50–60°F), getting a bit of a ‘sticky‘ feeling against the polyester liner. There is also a risk of condensation buildup during humid nights.
Features Analysis
The Free-Flow zipper system is a standout, allowing multiple configurations (full bag, quilt, or wearable blanket), though some find it finicky. The semi-rectangular design balances space and warmth well, and the ability to zip two bags together for couples is a clever perk. Dual storage options (compression sack + vented cube) help maintain loft long-term. The right-side-only zipper can feel unnatural, though, and there may be issues of minor down leakage near the seams. We also noted a slight initial odor from the down, which is common with untreated natural materials but note that it’s worth airing out before first use.
Construction and Durability
Built with a recycled 20D polyester shell and RDS-certified down, the Trek Down feels well-made for its weight (3 lbs 2.7 oz). The zippers are robust, though one be careful regarless so it doesn’t snag. The fabric strikes a balance between lightweight and durable, though we do kind of wish it had a tougher outer layer for rough use. It seems quite long-lasting, however, the polyester liner’s clamminess in humid conditions and occasional down leakage are worth noting.
Final Verdict
The Trek Down 15°F is a fantastic choice for car campers, overlanders and casual backpackers who are looking for something comfortable rather than being ultralight and minimal. Its roomy cut, versatile zipper system and reliable warmth make it great for three-season trips, especially for those who sleep cold or move around at night. Just don’t expect it to replace a true four-season bag or perform flawlessly in muggy climates.
Why not visit our list of the Top 5 Sleeping Bags of 2025 to see how Sea to Summit Trek Down compares?
Water & Outdoors reviews are written by our staff writers, who combined have over fifty years of experience on the water and outdoors. We may earn commissions if you choose to buy through a link you’ve clicked on our website, however this does not influence our reviews. For more information, please see our Editorial Policies.