Mt Washington 4 0°F Winter Hammock Underquilt

The Mt Washington 4 is JRB's 0°F winter hammock underquilt — and it ships with 15.52 oz of 850FP down when 11.4 oz is all this quilt's chambers require to hit 0°F. That extra 4.1 oz is a paid upgrade almost everywhere else. Here it's standard. Dual Differential Contoured Radial Baffles — the construction we invented — plus the JRB Suspension System and storage bag, handmade in the USA.

15.52 oz of Down. The Base Fill Rate Is 11.4. The Other 4.1 Is Free.

Shop a 0°F underquilt anywhere else and you'll find an option called overfill or overstuff — extra down beyond the base fill rate the temperature rating requires. Experienced hammock campers add it every time, because down loses loft as it picks up body oils, trail dust and humidity, and a quilt filled to exactly its base rate starts underperforming its rating within a season or two. Overstuff is what keeps a 0°F quilt a 0°F quilt in year five.

This is not a bespoke, built-to-your-measurements service anyone is paying a premium for. It's their standard catalogue quilt, with an upcharge of $10 to $15 per ounce attached to the one specification that decides whether it's still warm in five years. And because they hold no stock, you wait six to eight weeks for it either way — the overstuff just costs more on top.

Every Mt Washington 4 leaves our Pennsylvania shop with 4.1 oz of it already in — 36% above its base fill rate. We don't charge for it, we don't hide it behind a dropdown, and we don't build a quilt without it.

We don't call it overstuff. We call it optimized fill.

The word "overstuff" only works if you accept the premise buried underneath it: that a quilt's standard fill should be the bare minimum that hits the number on the day it ships, and that anything past that is a luxury you pay extra for. We don't accept that premise. A stock quilt should perform at its rating out of the box and still perform at its rating in its fifth season, with nothing added and nothing upsold. That isn't a deluxe option. That's the job.

So we build every quilt to the fill it should have had in the first place and put one price on it. We use the industry's word on this page only because you need it to run the comparison — it's the label on their dropdown, not ours. On our bench it isn't overstuff. It's just the fill.

What 36% Actually Buys You — and What It Doesn't

It does not make the quilt loftier. We'll be straight about that, because plenty of marketing implies otherwise. The Mt Washington 4 lofts to 3.5 inches, which is simply the loft a 0°F quilt is built to have — a chamber filled to exactly its base fill rate reaches the same 3.5 inches the day it's sewn. Lay two quilts side by side out of the bag and you would not see a difference.

The difference is everything that happens after that.

Down that has room to move, moves. A chamber filled only to its base rate has slack in it. Every night you shift in the hammock, every time the quilt gets stuffed and unstuffed, the down migrates — drifting to one side of the chamber and leaving the other side thin. That's the origin of most cold spots, and it's why people describe a quilt as one that "used to be warmer." Packing a chamber 36% fuller leaves the down far less room to travel, so it stays where it was sewn to be.

Down loses loft as it ages. Body oils, trail dust and humidity collect in the plumules over time, and loft falls off years before a quilt looks worn out. A quilt filled to exactly its rating has no margin for that; it starts sleeping colder than its label within a couple of seasons. The 36% is that margin. It's the reason we'll still call this a 0°F quilt in its fifth winter.

So you aren't buying a warmer quilt than the number on the label says. You're buying a quilt that is still that warm once you've actually used it. At 0°F that margin matters more than on any other quilt we build, because a quilt that has quietly drifted to a 10°F reality is a problem you discover at two in the morning.

Here's our arithmetic. Check that too.

The Mt Washington 4 is 42″ wide and 77″ long, divided into 11 differential-cut chambers, each 7″ long at 3″ of baffle wall height. That's 882 cubic inches per chamber and 9,702 cubic inches of internal volume.

Fill power is the number of cubic inches one ounce of down fills when fully lofted. So:

• 9,702 cu in ÷ 850 fill power = 11.4 oz — the base fill rate, the down this quilt needs to reach 0°F
• × 1.36 overstuff = 15.52 oz of down actually in the quilt (440.1 g, if you'd rather weigh it)
• The difference, 4.1 oz, is what other makers charge $41 to $62 to add

Every number in that calculation is published below in the specs. We're not aware of another quilt maker who publishes chamber count, baffle wall height, internal volume and base fill rate at all — which is precisely why a straight comparison between two down quilts is normally so hard to make.

What it costs to match this quilt elsewhere

Overstuff pricing reflects the published per-ounce upgrade rates on the standard catalogue quilts of major US quilt makers as of August 2026. We're not naming names — go price one up and check the math yourself. That's the point.

How to compare two underquilts honestly

Fill weight on its own means nothing, and any shop quoting it without dimensions is quoting a number you can't use. A quilt needs down in proportion to its internal volume — baffle wall height × chamber length × width, times the number of chambers. Ten ounces in a narrow 3/4-length quilt is a completely different quilt from ten ounces spread across a full-length shell. Same number, opposite outcome.

Here's the sequence that actually works:

1. Start with the geometry. Width, length, baffle wall height, and how many chambers. Those numbers give you internal volume — the space that has to be filled with lofted down. Ours is 9,702 cubic inches. Get the same figure for anything you're comparing, or you're not comparing anything.
2. Divide by fill power. Volume ÷ fill power = the base fill rate, the ounces that specific quilt needs to hit its rating. Ours is 9,702 ÷ 850 = 11.4 oz. Higher fill power means fewer ounces for the same volume — that's where weight savings come from, not from putting less down in the quilt.
3. Then ask how far above the base fill rate it's actually stuffed. This is the one number that compares across quilts of different sizes, because it's a ratio rather than a raw weight — and it's the number that tells you how long the quilt will hold the rating printed on its label. Ours is +36%, standard on every differential-baffle quilt we build. Most quilts ship at 0% over as standard, and the difference is sold back to you by the ounce.

Two quilts, same volume, same fill power, same rating: out of the bag they will measure the same loft. The one with more down in it is the one that still measures it in five years. Ask us for our chamber count, our base fill rate, or our overstuff percentage and we'll just tell you — they're all printed in the specs below, which is more than most makers will put in writing.

Built for Winter Hammock Campers Who Won't Let 0°F Call Off a Hang

Sleeping in a hammock compresses every bit of insulation beneath your body flat under your weight — and compressed down does not insulate. A sleeping bag used underneath simply cannot solve this problem. An underquilt hangs freely below the hammock shell, never touching you, so the down stays fully lofted and delivers its rated insulation from below. At 0°F there is no margin for a system that underperforms, and that is the whole reason this quilt is built the way it is.

How It's Built: Dual Differential Cut — The Construction We Invented

The Mt Washington 4 is built with Dual Differential Contoured Radial Baffles. We invented that construction at Jacks R Better, and it is the thing that separates a purpose-built underquilt from a top quilt repurposed underneath. The inner shell is cut smaller than the outer shell so the quilt conforms naturally to the curved underside of the hammock as it hangs, without the two shells pulling together at the edges and compressing the down. The baffles run radially to follow the contour of your body, keeping loft height constant from head to foot. This is why a differential-cut underquilt runs at its rated temperature when a flat quilt hung beneath a hammock would leave you cold — particularly in winter, when there is no margin for cold spots. We have been building underquilts this way since 2004, which is longer than most of the brands you are cross-shopping have existed.

The 11 contoured radial chambers run the 77″ length of the quilt on 3″ baffle walls across the full 42″ width, lofting to 3.5″. That is a full inch more loft than our three-season quilt carries, and it is where the 0°F rating comes from — not from a different construction or a different grade of down, but from taller chambers holding more air further off your body.

Suspension is via adjustable shock-cord loops at each end. Cinch the ends tight for a sealed hang on the coldest nights; loosen slightly to vent when the temperature rises. Setup takes under a minute and works on all gathered-end and bridge hammocks — ENO, Hennessy, Warbonnet, Dutchware Chameleon, and most other brands and DIY builds. The suspension system is included.

The shell is 1.1 oz taffeta with a DWR coating on both inner and outer layers. Every Mt Washington 4 ships in a storage bag that does not compress the down — keep the quilt in it between trips for long-term loft preservation.

Named for the Trail

Mount Washington, at 6,288 feet, is the highest peak in the northeastern United States. The summit weather observatory recorded a wind gust of 231 miles per hour in April 1934 — a world record that stood for 62 years. Temperatures drop below freezing every month of the year. The mountain's motto is not a figure of speech: Home of the World's Worst Weather. The Appalachian Trail crosses the Presidential Range just below the summit, exposed above treeline for miles with no shelter from whatever the mountain has in store.

The Mt Washington 4 carries that name because it was built for the same principle: some conditions don't negotiate, and preparation is the only variable you control. This underquilt was built for the nights when you need it to work.

Handmade in the USA by Jacks R Better, sewn in Pennsylvania — making quilts since 2004. In-stock quilts ship the same or next business day. If it's sold out, order anyway — that puts you in the build queue, and we'll sew yours and ship it in about 2–4 weeks. Finished quilts go to the people already in line, so waiting for one to reappear on the shelf usually means waiting longer.