The single most important decision when buying a hammock underquilt isn't brand or fill weight — it's temperature rating. Get it right and you sleep warm on the coldest night of your trip. Get it wrong and no amount of quilt on top makes up for the cold air stealing heat from underneath you. Jacks R Better invented the hammock underquilt back in 2004, and this is the same advice we give every customer: match the rating to the coldest night you'll realistically hang out in.
Why underquilt temperature matters more than anything else
The three ratings, and who each is for
A quick note before the ratings: many Jacks R Better quilts are multifunction — they work as a top quilt or hang below your hammock as an underquilt with the underquilt suspension kit, so one quilt can cover your whole sleep system. At each rating below you'll find both dedicated underquilts and a multifunction quilt, each offered in two builds — our standard 850-fill quilts, or the premium Ultralight line: 1000-fill-power down in a feather-light 10D shell, the lightest and most packable quilts we make.
40°F — summer & warm shoulder season
For warm-weather hangs and summer backpacking where lows stay above roughly 45°F. Our 40°F pick is the Shenandoah 40°F — a multifunction quilt that works as a top quilt on the ground or hangs below the hammock as a summer underquilt with the suspension kit. For the lightest, most packable option, step up to the premium Shenandoah Ultralight 40°F — 1000-fill down in a 10D shell. Browse the full underquilt collection too.
20°F — the three-season sweet spot (buy this if you buy one)
A 20°F underquilt covers spring, summer, and fall for most hangers — the most versatile single choice, and the one to start with if you're unsure. For a dedicated underquilt, look at The Nest 20°F (sized for Hennessy hammocks), the full-length Mt Washington 3 20°F, or the lighter 3/4-length Greylock 3 20°F. Or go multifunction with the Hudson River 20°F — a quilt that doubles as a top quilt and a 20° underquilt — in standard 850-fill, or the premium 1000-fill Hudson River Ultralight 20°F for the lowest weight.
0°F — winter & deep cold
When the temperature drops below freezing and you're chasing winter hangs, step up to a 0°F underquilt. These carry more down for true cold-weather warmth with no cold spots. For a dedicated underquilt, see the Winter Nest 0°F, the full-length Mt Washington 4 0°F, or the 3/4-length Greylock 4 0°F. Or go multifunction with the Old Rag Mountain 0°F — it also works as a top quilt — in standard 850-fill, or the premium 1000-fill Old Rag Mountain Ultralight 0°F for the lowest weight.
Premium — the Ultralight line. Every rating above also comes in an Ultralight build: 1000-fill-power RDS-certified down in a 10D (0.67 oz/yd²) shell — the lightest, most packable quilts we make, for when every ounce counts. Shop the Ultralight line →
Quick-pick table
| If your coldest night is… | Choose | Good picks |
|---|---|---|
| 45°F and up | 40°F | Shenandoah 40 (multifunction) · 850FP or 1000FP UL |
| 25–45°F (most 3-season) | 20°F | The Nest · Mt Washington 3 · Greylock 3 · Hudson River (multifunction) |
| Below 25°F / winter | 0°F | Winter Nest · Mt Washington 4 · Greylock 4 · Old Rag (multifunction) |
Can an underquilt be "too warm"? Not really — and it changes how you buy
Here's the part most people don't expect: unlike a top quilt or a sleeping bag, you simply don't overheat from an underquilt — even one rated far warmer than the night calls for, even fully closed. A bag or top quilt seals heat all the way around your body, so too much warmth leaves you sweating and kicking it off. An underquilt hangs below the hammock and warms only your back — the rest of you stays open to the air, so there's no sealed pocket to trap heat. Even closed up, it won't cook you.
So what's venting for? Comfort on the way in, not temperature control. If you climb into the hammock hot — sweaty from pitching camp on a warm night — cracking the ends open works like air conditioning, drawing cool air under your back until you settle. It's a nice-to-have, not a necessity — and it can overshoot.
What that means when you're buying: when you're between two ratings, size up. Erring warmer costs you nothing on hot nights but saves you on cold ones — a warm underquilt quietly covers a far bigger temperature range than the same-rated top quilt ever could.
We know because we've lived it. Don “DGrav” Gravatt — our owner, lead field-tester since 2008, and the same guy who answers the phone, replies to your emails, and shows up at the hangs and events — hung nothing but a 0°F Mt Washington 4 for two years straight, through lows of −16°F and highs of 91°F and humid, and never once overheated. In fact, on the hottest, stickiest nights, using that air-conditioning trick — ends cracked open to cool off going to bed hot — usually overshot: he'd wake up chilled and reach down to close them again. Closed up on a 91° night, that 0°F underquilt was just right. Too-cold happens from below; too-hot basically doesn't.
A note on full-length vs 3/4-length
Full-length underquilts cover you head to toe; 3/4-length underquilts save weight and pack size by stopping at your knees (you pad your feet with a pack or spare clothing). For winter, most people prefer full-length. For ultralight three-season trips, a 3/4 like the Greylock is a smart weight cut.
Underquilt temperature FAQ
What temperature hammock underquilt do I need?
Pick the rating for the coldest night you'll realistically sleep out in. A 20°F underquilt is the most versatile single choice for three-season hammock camping; go 40°F for summer-only, or 0°F for winter.
Can I use a 20°F underquilt in summer?
Yes — a 20°F underquilt has adjustable suspension, so you can loosen it slightly and vent for warmer nights. It's why the 20°F is such a popular do-it-all pick.
Can a hammock underquilt be too warm?
Not the way a sleeping bag can. It warms only your back while the rest of you stays open to the air, so there's no trapped pocket of heat to build up — even fully closed on a hot night, a warm underquilt won't overheat you, and you don't need to vent it. That's exactly why sizing up is a safe bet: you're covered when it's cold and you still won't cook when it's hot.
Do I still need a top quilt with an underquilt?
Yes. The underquilt handles the cold air below you; a top quilt keeps the warmth in from above. Together they're a full hammock sleep system. Not sure where to start? Read our Best Hammock Underquilts guide.
Every Jacks R Better underquilt is handmade in the USA with RDS-certified down — from the crew that built the first commercially available hammock underquilt in 2004. Sleep Better. Adventure Better.
Related underquilt guides: How to Hang a Hammock Underquilt · Which Underquilt Fits Your Hammock (ENO, Hennessy, Warbonnet) · Underquilt vs. Sleeping Pad.