Greylock 4 0°F Winter 3/4 Hammock Underquilt

At 22 oz, the Greylock 4 is JRB's lightest 0°F hammock underquilt — and it still ships with 11.29 oz of 850FP down when 8.3 oz is all this quilt's chambers require to hit 0°F. That extra 3 oz is a paid upgrade almost everywhere else. Here it's standard, even on our lightest winter quilt. Dual Differential Contoured Radial Baffles — the construction we invented — plus full-length channeled shock cord suspension and a storage bag, handmade in the USA.

11.29 oz of Down. The Base Fill Rate Is 8.3. The Other 3.0 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 Greylock 4 leaves our Pennsylvania shop with 3.0 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 Greylock 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 three-season quilt, 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 Greylock 4 is 42″ wide and 56″ long, divided into 8 differential-cut chambers, each 7″ long at 3″ of baffle wall height. That's 882 cubic inches per chamber and 7,056 cubic inches of internal volume.

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

• 7,056 cu in ÷ 850 fill power = 8.3 oz — the base fill rate, the down this quilt needs to reach 0°F
• × 1.36 overstuff = 11.29 oz of down actually in the quilt (320.1 g, if you'd rather weigh it)
• The difference, 3.0 oz, is what other makers charge $30 to $45 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 7,056 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 7,056 ÷ 850 = 8.3 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 Want 0°F Bottom Insulation at the Lowest Possible Weight

The full-length Mt Washington 4 covers you from head to foot at 0°F. The Greylock 4 covers your torso and hips — where you lose the most heat — and lets you use a sit pad or pack back panel for your lower legs and feet. At 56 inches long and 22 oz, it delivers a true 0°F bottom insulation rating at nearly 3 oz less than the full-length version.

Cutting length is the honest way to save weight in a winter quilt. Cutting fill is not, and at 0°F the consequences arrive faster — a quilt built to the bare minimum drifts off its rating within a couple of seasons and you find out about it in January. The Greylock 4 is short and filled 36% over: 11.29 oz of down in a quilt whose chambers only require 8.3. You give up coverage, not longevity.

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

The Greylock 4 is built with Dual Differential Contoured Radial Baffles. We invented that construction at Jacks R Better and have been building underquilts this way since 2004, which is longer than most of the brands you are cross-shopping have existed. 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 across the length of the quilt. At 0°F, cold spots are not recoverable — the differential cut is what ensures every chamber stays full all night.

The 8 contoured radial chambers run the 56″ 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 the three-season Greylock 3 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 full-length channeled shock cord with adjustable ends and corner mounting tabs for users who prefer the traditional JRB corner suspension method. Cinch the ends tight for a sealed hang on the coldest nights; loosen slightly to vent when the temperature allows. Setup takes under a minute on all gathered-end and bridge hammocks — ENO, Hennessy, Warbonnet, Dutchware Chameleon, and most DIY builds.

The shell is 1.1 oz taffeta with a DWR coating. Every Greylock 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 Greylock, at 3,491 feet, is the highest peak in Massachusetts. The Appalachian Trail crosses the summit, where the weather rolls in fast and the temperature drops well below what the valley suggests. In January, the summit sees sustained winds, icing, and temperatures that make a 0°F rating a requirement, not a margin. Northbound thru-hikers who push through Greylock in late May and June still find winter-like conditions at the top.

The Greylock 4 carries that name because it was built for the same principle: carry only what you need, but make sure what you carry does the job at 0°F. Torso insulation where you lose heat. A sit pad for the rest. Nothing extra.

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.

Note: 3/4 underquilt users typically use a sit pad or pack back panel for foot and lower leg insulation. For full-length coverage, see the Mt Washington 4.