DIY Underquilt: A Complete Build Guide

By topquilt.com · Updated Oct 21, 2026 · 7 min read

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Building a DIY underquilt is one of the most rewarding hammock projects. It's also simpler than it looks: an underquilt has no footbox, no zippers and no complicated shape. You're essentially making an insulated rectangle that gathers at the ends and hangs under your hammock. With a home sewing machine and a weekend or two, you can build a quilt that fits your hammock exactly and costs noticeably less than most commercial options.

This guide covers choosing insulation, planning dimensions, differential cut, channels, suspension and a full materials list. If you've already built a top quilt, much of this will feel familiar; see our DIY top quilt guide for overlapping techniques.

Step 1: Choose your insulation (down vs APEX)

The choice of insulation affects every other step. Here's how the two most common DIY options compare:

APEX is a great first build and a strong choice for wet climates. Down rewards the extra effort with a lighter, smaller quilt for cold weather. For more detail on the trade-offs, read down vs synthetic underquilts and our guide to Climashield APEX insulation.

APEX weights and rough temperature targets

APEX is sold by weight per square yard. Commonly cited sleeping-comfort estimates for hammock use are roughly: 2.5 oz/yd² for summer (around 50°F), 5.0 oz/yd² for three-season (around 30-40°F), and 7.5 oz/yd² or stacked layers for colder nights. These are estimates, not test results, and personal metabolism, wind and sleepwear move them a lot. When in doubt, go one step warmer.

Down fill planning

For down, the target is loft height. A three-season underquilt commonly aims for around 2 to 2.5 inches of loft; colder builds aim higher. Fill weight depends on fill power, dimensions and overfill. Most DIYers use an online down calculator, then add some overfill (often 10-30%) to account for down settling and the compression of the hammock's curve. Our fill weight and overfill page explains the math.

Step 2: Plan dimensions and length

Size depends on your hammock and how you sleep. Typical starting points:

Remember that the end channels gather fabric, so finished coverage feels shorter than the flat length. Add a few inches for channels and seam allowance. If you're unsure which length suits you, see full vs 3/4 underquilt and our underquilt sizing guide.

Step 3: Understand the differential cut

An underquilt hangs in a curve beneath you. On a curve, the inner surface (closest to the hammock) has a smaller radius than the outer surface (facing the ground). If both shells are cut the same size, the inner shell bunches and the outer shell pulls tight, squashing the insulation.

A differential cut makes the inner shell slightly narrower than the outer shell so both lie smoothly when curved, letting the insulation loft fully. DIY builders commonly use a differential of a few inches across the width. Some also add a smaller lengthwise differential.

It's optional. Many perfectly warm DIY quilts skip it, especially APEX builds, where the material resists compression better. If you use it with down, cut the baffles to match: baffle strips are attached to two shells of different widths, so channel spacing on the inner shell is slightly smaller than on the outer.

Step 4: Plan channels (down builds)

Down needs to be contained, or it will drift and leave cold spots. That's what baffles do: internal walls of light mesh or noseeum fabric that create channels. See quilt baffles explained for background.

Common decisions:

• Baffle direction: Many DIY underquilts run channels across the width of the quilt; others run them lengthwise. Cross-wise channels make it easy to shift down toward the edges or center; lengthwise channels can reduce down migration toward the ends when the quilt is cinched. Both work.
• Baffle height: Usually around 2-2.5 inches for three-season, taller for winter.
• Channel spacing: Often 5-7 inches. Narrower channels control down better but add sewing time and weight.
• Channel closure: Leave one end open for stuffing, then close it with a seam after filling.

For an APEX underquilt, there are no baffles. Just sandwich the insulation between the shells and sew around the edges, adding a few quilting lines if the maker of your insulation recommends it for your size.

Step 5: Build the quilt body

1. Cut shells. Cut inner and outer shells, adding seam allowance and channel allowance at each end. Mark baffle lines on both shells with a fabric pen.
2. Sew baffles (down only). Sew baffle strips to one shell along the marked lines, then attach the other side of each baffle to the second shell. Take your time; this is where most errors happen.
3. Join the shells. Sew the long edges together, inside out, leaving channel openings accessible if needed. For APEX, lay the insulation on the shells and sew all three layers at the edges.
4. Turn and stuff. Turn the quilt right side out. For down, weigh each channel's fill with a digital scale and stuff it in batches. Work in a small, still room; a plastic bag over the down container helps reduce mess.
5. Close the channels. Sew the open ends of each channel closed after stuffing.
6. Form end channels. Fold each short end over and sew a channel wide enough for shock cord or webbing.

Step 6: Add suspension

Suspension is what makes a flat insulated rectangle into an underquilt. Most DIY builds use:

• End channels with shock cord cinched by a cord lock, shaping each end into a cradle.
• Main suspension lines from each end channel to the hammock ends or ridgeline, using static line with a short shock cord section for flex.
• Side pull-outs (optional): small grosgrain loops or shock cord along the long edges to seal gaps around shoulders.
• Connectors: small carabiners, toggles or prusik loops.

Our underquilt suspension explained guide covers the trade-off between shock cord and static line in detail, so you can rig your DIY quilt the way you like it.

Materials list

Where to buy materials

Specialty DIY suppliers stock the hard-to-find items like downproof shell fabrics, APEX insulation, baffle mesh and quality down. Ripstop by the Roll is a popular source for hammock and quilt fabrics, insulation and hardware, and many DIYers buy a complete fabric set there.

For general supplies, Amazon is convenient:

• Lightweight ripstop nylon for mock-ups or budget shells
• Climashield APEX insulation (availability varies)
• 1/8 in shock cord
• Mini cord locks
• Small-diameter dyneema cord
• Digital scale with gram resolution
• Rotary cutter and cutting mat

Our quilt making materials page covers fabric weights and choices in more detail.

Common DIY mistakes to avoid

• Underfilling down. Down settles. Add overfill so the quilt actually reaches its target loft in use.
• Cutting too narrow. Narrow quilts leave gaps at the shoulders, especially in wide hammocks. Measure your actual lay with a mock-up first.
• Skipping reinforcement. Suspension points take load; reinforce them with grosgrain or extra stitching.
• Using non-downproof fabric. Down will slowly leak through some fabrics. Use fabric sold as downproof for down builds.
• Making everything too tight. End cinches and side pull-outs should shape the quilt, not crush it.

Testing and adjusting your DIY underquilt

Before you rely on it in the backcountry, hang it in a backyard or a nearby campsite on a cool night. Check for cold spots at the shoulders, hips and feet, and tweak the suspension using the steps in how to hang an underquilt. If you feel a persistent cold spot under your hips, read cold butt syndrome for fixes.

Once it's dialed in, look after it like any other quilt; our guide to washing an underquilt covers care. And if you decide building isn't for you after all, our roundup of the best underquilts and best budget underquilts covers good off-the-shelf options.