GEMINI Hammock Underquilt Logo

The GEMINI Hammock Underquilt

How to make a DIY, no-sew, all-season, convertible, down underquilt for $65 and love the results.

Diagram for GEMINI quilt design.

Converts to match any season:


This do-it-yourself hammock underquilt design is meant for persons new to hammock camping that need an easy and affordable underquilt that actually works. It is made from 2 down blankets sold at Costco or Bed Bath & Beyond and converts into 3 different modes to match any season. It puts the best ideas on the topic into one project that is easy, accessible, affordable, and highly effective.

This design totally out-competes entry level alternatives like the Poncho-Liner Underquilt (PLUQ), sleeping bag conversions, SnugPak underblankets, and imported junk you find on Amazon.

Finished GEMINI quilt with triple-layer sash.

Design Features

5 inch loft on the ground. Average 2-3 inch loft when hung.

Design Philosophy / Pros & Cons

There are lots of DIY Costco underquilt conversions already out there. This design attempts to put together some of the best ideas on the topic and make it easy for persons just getting into hammocking.

This design is meant to be affordable, easy, and high-performing. To achieve this, we use off-the-shelf items and inexpensive tools, a no-sew snap-together design, triple-layered construction for warmth, and an elastic clew suspension to avoid fiddly adjustments and cold spots.

Everything is a trade-off, though. This design weighs in at a little over 2 pounds. It won't qualify as "ultralight", but at it's price-point it's nearly unbeatable. Also, don't expect 900 fill power down, dry down, or waterproof materials you might expect from pricey cottage vendors. I love pricey cottage vendors, but if you can't afford that, then this is your next best thing.

Finished quilt hung on Warbonnet Blackbird.

This design is also meant to be convertible. Because it uses two blankets layered together, you get some sweet options at no additional cost:


Construction Guide

Download and print for quick reference when making your quilt. Prints on standard 8.5x11 in color.

Download PDF (1.0 MB)

True to it's mythological name, the GEMINI underquilt is made from two identical Costco down throw blankets. To make the directions more clear we're going to call these after their original Greek names: "Pollux" is the main underquilt, and "Castor" is the convertible secondary blanket.

Total estimated construction time for the complete set is about 6 hours.

Okay, let's build this bad boy...

Materials & Tools

You will need:

Making "Pollux"

Rip out all of the short seams leaving long baffles.

Rip Seams

Each blanket is made of 12x14 5" squares. We are going to remove all of the short, widthwise seams. This will leave you with long, lengthwise baffles of down. Removing seams helps it loft much higher.

For n00bs: If you've never used a seam ripper before, listen up: Each seam has two sides. One side is a thread that loops in and out of the fabric. The other side is a straight thread that is captured by the loops from the other side. Find the side with the straight thread. Use the seam ripper tool to snip each square once at the seam and once in the middle. Use tweezers to firmly pull the thread straight out. Once the straight thread is remove, you will find the other half of the thread on the reverse side completely free. This should take you an hour or two. Put some music on, pour a beverage of your choice, and lets get to work.

Rip out all of the short seams leaving long baffles.

Clew Attachment Snaps

Next we are going to add the attachment points for the clew suspensions.

Cut your grosgrain ribbon into 26 4-inch segments. Use a candle flame to melt the ends. This prevents it from fraying.

Next, rivet the ribbons to the blanket at the corners and the top of each seam as you see below:

Put snaps and ribbons at tops of corners and seams. Assembly diagram for snap-on attachment points for underquilt clew suspension.
Use the awl to pierce the fabric.
Insert a KAM snap cap and socket.
Use the KAM snap pliers to affix the socket.
Repeat process for the stud snap.
Finished clew attachment snap loop.
Clew attachment points have a built-in pull tab from the excess ribbon.
Finished clew snap loop in closed position.

Make Clews

This part is easy. You need a board and two nails. Put the nails firmly in the board about 21" apart. Put your keyring or mini-carabiner on one nail.

Tie one end of the shock cord to the ring with a simple slip knot, leaving at least an 8" tail. Go around the second nail with the cord and back through the ring. Do this 13 times. Use light, even tension.

After the cord takes the final trip through the ring, make a temporary whipping to hold it together. Leave another 8" tail and cut the shock cord.

Make two of these.

Later, after you have tested the completed assembly, you can remove the temporary whipping and whip the two tail ends of the shock cord into a Western Country Whipping. Alternatively, you can weave them together with a Shouldered Sword Mat if you feel like being fancy.

Tip: Several users have found that the quilt shapes better if you leave the first and last nettles about 3 inches shorter than the others. This puts more tension across the edges of the quilt.

A board with some nails is all you need.
Use a mini carabiner to make it easier to pass the cord through.
Use light, even tension.
Wrap around both ends 13 times making 13 loop nettles.
Tie it with a temporary whipping until you decide to finalize it.
Notes on hammock size:

These directions are for a 10ft+ hammock. If you want to custom tailor your GEMINI quilt to a specific hammock, use the following chart for the best fit:

Attach Clews

For each side, take each loop of the clew (AKA a "nettle") and connect it to an attachment snap on the blanket. You should have 13 nettles hooked into 13 snaps.

Tie a 2-foot piece of any ol' cord to the end of the ring. Use this to tie to the hammock. Using this extra bit of cord gives you the option of adjusting the positions and tension of the quilt later.

Hang it up and try it out!

Attach a simple cord to the ring to use for attaching to the hammock and adjusting tension.
Attach quilt to hammock with a simple slip knot.
Finished quilt hung up.

Making "Castor"

"Castor" is the secondary, inner blanket. Making Castor is much faster than making Pollux.

Second blanket with ripped seams.

Rip Seams

Rip the short seams exactly the same as the first blanket. You should be getting good at this now.

Add Snaps

Add snaps as shown in the diagram. This is easy to mess up if you are not paying attention. I recommend you mark each spot with a sticker or piece of tape to show which is a socket or stud, face up or down.

VERSION 2.0 UPDATE: v2.0 uses a "Tetra-Pak" inspired shaped footbox. The snap pattern for this is a bit more convoluted than the regular flat-seamed version 1.0 topquilt. If you want the old version of the Castor blanket, just use this snap pattern instead.

Optional Tip: Use two different colors of snaps to differentiate between the ones used for attaching the clews and the rest used for converting to a topquilt.

Just a bunch of snaps. You can do this. I have faith in you.

That's it. You're done. Now the fun part ...

How To Hang It

Summer Mode

Just tie the Pollux blanket up by itself and turn the Castor blanket into a standalone topquilt. The sides will snap together and the footbox should snap closed.

VERSION 2.0 UPDATE: v2.0 uses a "Tetra-Pak" inspired shaped footbox. Start by snapping the long edges together to form a tube. Snap the middle of the footbox together (3 snaps). Roll the bottom up (2 snaps). Roll the top down (2 snaps).

The footbox on the GEMINI version 2.0 topquilt folds up like a Tetra-Pak box. New Tetra-Pak footbox has less dead space inside and fits human feet better.

Tips for Summer mode: Unfortunately, we are dealing with a sewn-through design on a single blanket. This means that you may feel coolness along the seams under the hammock. To mitigate this, there are a couple of options:

Spring / Fall Mode

Simply line up the blankets and connect the snaps from Pollux onto Castor, keeping the clew nettle captured underneath. That's it. The snaps on Castor are designed to offset the baffles on Pollux, so the two blankets create a great layering effect. Simple and effective. It's also a great width for side sleeping.

Note: The are 11 snaps on Castor and 13 on Pollux to create an offset. Center the blanket when joining the two together (i.e. skip the ones on the corners).

Line the blankets up and snap together.
Line up blankets with Castor on top.
Unsnap Pollux.
Snap clew onto Castor. That's it.

Winter Mode

Join the blankets together, as in Spring/Fall mode, but detach half of the snaps on Castor and fold the corners together to create a triple-layer asymmetric sash. You are now armored against the cold and you did it for cheap!

Triple layer Winter mode, ready to hang. Line up blankets with Castor on top.

Triple layer Winter mode, ready to hang.

Additional Resources

Visit the thread on for more info and pictures of GEMINI quilts in the wild.

This design is based on research and development on elastic clew suspensions for hammock underquilts. You can read my original article on clew suspensions and subsequent discussion on Hammock Forums.

Check out Boone's video series on how to construct a GEMINI underquilt from start to finish

Going Further

Officially, this is a no-sew design. However, if you are willing to do a little bit of sewing, you can take the design further. Adding "faux baffles" to Pollux is an easy way to get rid of exposed seams and retain heat. Search for "costco faux baffles" and you will find lots of instructions.

If you need to get fancy, you can finish your clews with a Shouldered Sword Mat instead of a whipping.

I recommend putting some kind of sock, sleeve, mesh, or rubber bands around the clews to prevent tangles during transport.

Add an underquilt protector to block the wind and retain heat even more.


I want to be very clear about what I mean by "all-season" and "winter mode". I would feel comfortable taking this setup into the Winters I experience where I live in the Pacific Northwest. This is not intended for Arctic Circle extreme blizzard conditions, etc.

I am purposefully not putting any kind of temperature rating on any of these configurations. Everyone sleeps differently. I don't want anyone to blame me for going out into sub-zero temps and freezing.

Use good judgement, people!


I didn't think of all of this on my own. Thanks to everyone who contributed ideas towards this design, too many to mention.

If you make this design and have feedback or improvements, please post something on

GEMINIs In The Wild:

GEMINI underquilt in the wild.


Thanks for reading. Happy hammocking!