Your sleep system is one of the Big 3, and the first fork in the road is bag vs. quilt. Then comes the question that actually determines warmth and weight: what's inside it. Here's how to think about both.
The core difference
A sleeping bag fully encloses you — a zipper up the side and an insulated hood. A quilt is open on the bottom, has no zipper and usually no hood, and straps to your sleeping pad instead.
Why do quilts weigh less? Because the insulation underneath you in a bag is crushed flat by your body weight and does nothing — you're carrying dead insulation plus a zipper and hood you may not need. A quilt deletes all of that and lets your pad do the insulating underneath (which is why a warm pad matters). The tradeoff: quilts can let in drafts if you thrash around, have a small learning curve, and suit some sleepers better than others.
How to choose between them
- Quilt — lightest option, great for warm sleepers, back/still sleepers, and 3-season temps. Best warmth-to-weight.
- Bag — better for cold sleepers, restless/side sleepers, and truly cold conditions where a sealed hood and draft-free enclosure matter.
See real examples in the best quilts and the best sleeping bags.
The fill: down vs. synthetic
This choice matters more than bag-vs-quilt for both warmth and price.
Down
Down is the fluffy under-plumage of ducks and geese, and it's the best natural insulator we have. Its warmth is measured by fill power — the volume in cubic inches that one ounce of down lofts to. Common ranges are 650, 800, and 900+. Higher fill power lofts more per ounce, so it takes less down to hit a given warmth — that's why 900-fill gear is lighter (and pricier) than 650-fill at the same temperature rating.
- Pros: best warmth-to-weight, extremely compressible, lasts 10+ years with care.
- Cons: expensive; loses loft when wet and dries slowly (though most modern down is treated to be water-resistant, or "hydrophobic").
- Ethics: look for the RDS (Responsible Down Standard), which certifies humane sourcing.
Synthetic
Synthetic fills are polyester fibers engineered to mimic down's loft. There are two broad styles: continuous filament (long strands — very durable and resists shifting; Climashield APEX is the popular ultralight version, common in cottage quilts) and short-staple (shorter fibers — softer and more packable but breaks down faster; PrimaLoft is a well-known example).
- Pros: much cheaper, keeps insulating when damp, dries fast, hypoallergenic.
- Cons: heavier and bulkier for the same warmth, and it slowly loses loft as it's compressed over its life.
Side by side
| Down | Synthetic | |
|---|---|---|
| Warmth-to-weight | Best | Good |
| When damp/wet | Loses loft, dries slowly | Still insulates, dries fast |
| Packed size | Very compressible | Bulkier |
| Lifespan | 10+ years with care | Loft fades over time |
| Cost | $$$ | $ |
Rule of thumb: down for the best weight and packability in dry-to-normal conditions; synthetic for wet climates, budgets, or when reliable warmth-while-damp matters most.
Reading temperature ratings
Standardized bag ratings (EN 13537 / ISO 23537) give several numbers. The two that matter:
- Comfort — the temperature a "cold sleeper" stays comfortable. Cold sleepers and many women should buy to this number.
- Limit — the temperature a "warm sleeper" can sleep, curled up. Marketing often headlines this one.
Important caveat: most quilts aren't EN/ISO tested, so cottage quilt temperature numbers can run optimistic. Whatever you buy, give yourself a margin — a bag or quilt rated ~10°F colder than the coldest night you expect is a safe bet.
Dial in your sleep system as part of the Big 3: open the pack builder →