There’s no standard for underquilt temperature ratings. So we built our own, transparent one — and we’re laying it out in full so you can check our work and hold us to it. We think every underquilt should be rated this way.
A sleeping bag can be lab-tested against an international standard (EN 13537 / ISO 23537). An underquilt can’t — the standard measures a mannequin on a sleeping pad, on the ground, and an underquilt hangs beneath a hammock, where there’s neither floor nor pad. The result: every underquilt rating out there is an estimate, and since nobody’s forced to show their work, a number can be anywhere from honest to pure marketing.
We think you deserve better than that. Here’s exactly how we arrive at our ratings. No black box.
Principle 1: We rate comfort, not limit
Temperature ratings come in more than one flavor. Comfort is the temperature where an average sleeper is genuinely comfortable. Limit is the temperature where a warm sleeper just barely avoids being cold, curled up tight — you survive, but you’re not enjoying it. The gap between the two is typically 5–6°C.
The easiest way to make a number look impressive is to quote the limit rating (or something colder still) and call it the product’s temperature. We do the opposite: our headline number is comfort. We publish the limit too, but as a secondary “technical limit” — never as the main figure. Better not to freeze on night one.
Principle 2: We calculate from loft — and calibrate against the honest ones
Warmth comes from loft (insulating thickness), and loft = fill power × fill weight. All our underquilts use 850FP down, so fill weight (grams of down) is the number that decides.
But we don’t pull a rating out of thin air — we calibrate against real reference products from manufacturers known for rating conservatively (American cottage makers like UGQ, Hammock Gear, Enlightened Equipment). Concretely: a full-length 850FP underquilt carrying roughly 164 grams of down per square meter corresponds to an honest −7°C limit rating (≈ −1 to −2°C comfort). We place our own models relative to that anchor — and check them against our own field data.
We deliberately don’t calibrate against the brands that inflate their numbers. (We checked: one well-known competitor rates an underquilt at −12°C comfort, when its down density honestly supports about −5°C — but only “when paired with a matching top quilt.” More on that below.)
Principle 3: We count coverage, not just grams
Two underquilts with identical fill weight can sleep completely differently if one is shorter or narrower than the other. So we use areal down density — grams of down per square meter — so size gets counted instead of hidden. Our underquilts are full-length, 208 × 142 cm = 2.95 m², longer and wider than many on the market. That means more continuous contact with the hammock and fewer cold spots — and it’s baked into how we set the rating.
What we don’t do
- No credit-stacking. We never quote a colder number “when paired with a matching top quilt” and credit the top quilt’s warmth to the underquilt. Our comfort number is the rating of the underside alone. A hammock system is two independent halves — under and top — and it’s only ever as warm as its weaker half, so pair the underquilt with top insulation that’s at least as warm, and the system reaches the number.
- We never claim “EN-tested.” That’s not possible for an underquilt (see above). If you see that claim anywhere, take it as a warning sign.
- We never quote limit as if it were comfort.
Our published ratings
| Model | Down (850FP) | Comfort | Technical limit |
|---|---|---|---|
| UQ300 | 300 g | +5°C | ~+2°C |
| UQ400 | 400 g | 0°C | ~−3°C |
| UQ500 | 500 g | −2°C (down to −5°C with a matching top quilt) | ~−6°C |
| UQ800 | 800 g | −10°C | ~−15°C (in ideal conditions) |
All full-length (208 × 142 cm), H-baffle construction, 850FP RDS-certified down.
We’re honest about the uncertainty
These are field-informed engineering estimates, not lab certificates — like every underquilt rating on the market. We set them as conservative ranges, calibrated against honest reference products, against the physics (loft → temperature), and against real field testing in Nordic cold. Actual warmth shifts with wind, fit, metabolism, and — above all — your top insulation. Our rule of thumb: budget roughly 5°C of margin, and be honest with yourself about the coldest night you actually plan to use it on.
An open invitation
We don’t think we’re the only ones capable of rating honestly. We think every underquilt should be rated this way — comfort as the headline number, calibrated against honest references, coverage counted, no credit-stacking, and full transparency about the method.
So here’s ours. Use it. Challenge it. Hold us to it. If you find a model where our number doesn’t hold up in the real world, we want to know — get in touch.
Want to see how it lands for you? Try the underquilt calculator, or read the full underquilt guide on comfort, limit and loft.