Making a Lightweight Camping Hammock Underquilt

Why an Underquilt Beats a Sleeping Bag in a Hammock

In a hammock, the insulation underneath you is crushed by your own body weight, and crushed insulation is almost worthless. That is why even a good three-season sleeping bag will leave you shivering at 5°C in a hammock, while the same bag feels toasty on the ground. The fix is simple: hang your warmth below the hammock, where the loft stays full and cold air never touches your back.

An underquilt does exactly that. Because it does not need to wrap around you, it can be substantially lighter and less bulky than the bag it replaces. A well-built synthetic underquilt of around 750–900 g will see you comfortably through a British three-season night, where the equivalent sleeping bag easily tops a kilogramme and fills half your pack.

Choosing Your Insulation

For UK conditions, continuous filament synthetic insulation is usually the sensible choice. It handles damp far better than down, dries quickly at camp, and does not need babysitting in a stuff sack. It is also much easier to sew, because you can stitch straight through it without creating cold spots through migration.

• 133 gsm — summer use, roughly 10°C and above. Light and packable.
• 200 gsm — the sweet spot for British three-season camping, comfortable to around 0°C with a decent top quilt.
• 266 gsm — winter and cold sleepers, but expect a bulkier pack.

If you do go for down, choose a high fill power (750+), use a calendered 10D or 15D shell to stop feathers escaping, and build proper baffles. Down wins on weight and pack size, but only if you can keep it dry — and in a Welsh valley in October, that is a big if.

Sizing and the Differential Cut

Measure your hammock first. A gathered-end hammock typically needs an underquilt around 1.8–2.0 m long and 1.1–1.3 m wide to cover shoulders to feet when you lie on the diagonal. Err on the generous side: a quilt that is 10 cm too wide adds almost no weight but prevents a lot of cold draughts.

The single most important construction detail is the differential cut. Make the outer shell roughly 10–15% larger in both dimensions than the inner shell. This lets the insulation loft to its full thickness without being squashed between two panels of equal size. Without it, your beautifully thick quilt will compress itself flat the moment it is hung.

Suspension That Actually Works

A good underquilt hugs the hammock without squeezing it. The trick is a two-part suspension.

• Primary: 3 mm shock cord threaded through a 2 cm channel at the head and foot ends, attached to the hammock's own suspension or to a structural ridgeline.
• Secondary: 2 mm shock cord running along each long edge, with cord locks, clipped to the hammock's gathered ends. This tensions the sides so the quilt stays snug when you shift position.

Set the primary cord so the quilt sits just beneath you with a finger's width of gap — enough to trap a layer of still, warm air, but not so loose that it sags away from your back. Adjust the secondary cord so the sides pull up around your shoulders and feet. A cold back usually means the quilt is too loose, not too thin.

Sewing It Together

Use a 10D or 15D ripstop nylon with a durable water repellent finish for both shells. It weighs around 35 gsm, handles abrasion better than it looks, and packs down small.

• Cut the inner shell to your target size and the outer shell 10–15% larger.
• Hem the long edges with a 1 cm double fold, then thread the secondary shock cord through.
• Fold and stitch 2 cm channels at the head and foot ends for the primary cord.
• Lay the insulation between the shells, tack it lightly along the long edges only, and stitch the ends closed.
• Add a small fabric collar — a short cone of shell material — at each end. These stop cold air rushing along the hammock body and are the difference between a good quilt and a great one.

Sew with a 70/10 needle and polyester thread at a 3–3.5 mm stitch length. Long stitches mean fewer perforations and less chance of tearing the light fabric.

Testing and Looking After It

Hang it in the garden on a cool night before you trust it on a trip. Check for gaps at the shoulders when you lie diagonally, and look for compression points where the quilt pulls tight against the hammock. Adjust the cord locks, then mark the positions with a permanent marker so you can find them again in the dark.

Store it loose, never compressed, and wash it sparingly with a technical cleaner — no fabric conditioner, which coats the fibres and kills the loft. Hang it to dry fully before packing away. Look after it and a well-made underquilt will outlast several sleeping bags and keep you warm on every trip from the Cairngorms to the Cornish coast.