Greylock 3 20°F Three-Season 3/4 Hammock Underquilt

At 17 oz, the Greylock 3 is JRB's lightest 20°F hammock underquilt — and it still ships with 36% more down than its chambers need to hit 20°F, at no extra charge. Dual Differential Contoured Radial Baffles — the construction we invented — plus full-length channeled shock cord suspension and a storage bag, handmade in the USA.

Built for Ultralight Hammock Campers Who Want 20°F Bottom Insulation at the Lowest Possible Weight

The full-length Mt Washington 3 covers you from head to foot. The Greylock 3 covers what matters most — your torso and hips — and saves the weight that would otherwise go to covering your lower legs and feet. At 56 inches long it runs from your shoulders to your knees, and most users pair it with a sit pad or a back panel from their pack underneath their lower legs. Full 20°F bottom insulation where it counts, at 17 oz.

Cutting length is the honest way to save weight in a down quilt. Cutting fill is not, and it is the more common one — a shorter quilt with the down thinned out to hit a weight target reads well on a spec sheet and goes cold on you in a season or two. The Greylock 3 is short and filled 36% over: 7.53 oz of down in a quilt whose chambers only require 5.5. You give up coverage, not longevity.

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

The Greylock 3 uses Dual Differential Contoured Radial Baffles — the same construction as the full-length Mt Washington series. We invented it at Jacks R Better and have been sewing underquilts this way since 2004. The inner shell is cut smaller than the outer shell, so the quilt conforms to the curved underside of a loaded hammock instead of the two shells pulling together at the edges and compressing the down between them. The baffles run radially to follow the contour of your body, which is what holds loft height constant from end to end as the hammock changes shape under you.

Suspension is full-length channeled shock cord with adjustable ends and corner mounting tabs — and you cannot hang it too tight. Because the outer shell is cut larger, it keeps its slack no matter how far you pull the suspension down, so tightening seals the edges against draughts instead of crushing the loft. You also cannot be too warm underneath — the same reason you sleep on the same mattress in July as in January. An underquilt warms only your back; the rest of you stays open to the air, so there is no sealed pocket to trap heat the way a sleeping bag does. Carrying more rating than the night calls for costs you nothing — here is how to pick between 40°, 20° and 0°F. Setup takes under a minute on all gathered-end and bridge hammocks — ENO, Hennessy, Warbonnet, Dutchware Chameleon, and most DIY builds.

Every Greylock 3 ships in a storage bag that does not compress the down.

Optimized Fill: 7.53 oz of Down Where 5.5 Would Do

Everyone else calls it overstuff and sells it by the ounce. We call it optimized fill, because a quilt filled only to its base rate fails two ways. The down has slack to move in, so it drifts to one side of a chamber and leaves the other side thin — and a thin chamber is a cold spot. And down loses loft as dirt, body oils and dust work into the plumules, so a quilt with no fill to spare drops below its rating within a season or two.

This quilt's chambers require 5.5 oz of 850FP down to reach 20°F. Every Greylock 3 ships with 7.53 oz — 36% over. Not an upgrade, not a dropdown, not priced separately. That extra 2.0 oz is what takes the slack out and supplies the margin — which is why we'll still call this a 20°F quilt in its fifth season. On a quilt this light, carrying this little down to begin with, that margin is the difference between an ultralight choice and a compromise.

Here's our arithmetic. Check it against anyone else's.

• 42″ × 56″, 8 chambers × 2″ baffle walls, lofting to 2.5″ = 4,704 cu in internal volume
• 4,704 ÷ 850 fill power = 5.5 oz base fill rate — the down this quilt needs to reach 20°F
• × 1.36 = 7.53 oz of down actually in the quilt (213.4 g, if you'd rather weigh it)

Those are the three numbers to ask any maker for. Matching this much fill elsewhere runs $20 to $30 on top of the listed price, and it is built to order. Ours is in the price and on the shelf. How the base fill rate is worked out, and how to run this comparison on anyone else's quilt.

Named for the Trail

Mount Greylock, at 3,491 feet, is the highest peak in Massachusetts. The Appalachian Trail crosses the summit, where clouds collect even on clear days in the valley below. The summit is exposed, the temperatures drop fast after dark, and the shoulder seasons bring the kind of damp cold that feels colder than the thermometer says. Spring thru-hikers push through Greylock in April and May — early enough that nights can still drop well below freezing at elevation.

The Greylock 3 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. 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 3.