The Perfect Fit for
Hammock Underquilts

Spandex gives your hammock underquilt a frustration free, perfectly form-fitting hang every time. Be done with cold spots and fiddly underquilts forever.

This article will teach you how to build an elastic spandex underquilt suspension. You can make a quilt from scratch or easily retrofit an existing quilt with stretch fabrics to get a perfect fit with no cold spots on every hang.

In this article:

Why Spandex?

Hammock underquilt owners frequently ask about how to make their quilts fit better, avoid cold-spots, and reduce fiddle-factor. You can get rid of all of these annoyances once and for all using spandex fabric.

With spandex there is no learning curve. No adjustments to be made. No "dialing it in". No realization at midnight that your quilt isn't fitted right and your butt is getting cold. You just set it and forget it! Spandex will make the quilt hug your hammock no matter how you lay in it.

The biggest failing of traditional shockcord side-channel underquilts is that they have no tension through the center of the quilt. This means the quilt sags and you are likely to experience cold spots where the blanket does not make even contact with the underside of the hammock.

The cure for this problem is elastic. Having elastic across the short edge of the quilt means you distribute tension across the entire blanket, providing you with a perfectly snug fit. Speaking of snug fits ...

Quick History

Using elastic fabric on an underquilt is not a new idea. In fact, it was used on the Speer SnugFit underquilt as far back as 2009. For whatever reason, this concept never caught on with either commercial vendors or do-it-yourselfers. This is likely due to the economics of labor involved for vendors and unfamiliarity among the DIY/MYOG crowd.

The truth however is that you can build a great underquilt using spandex fabrics for no additional cost and no additional effort. Why are people not already doing this?



There are three main categories of stretch fabrics we might look at for underquilt construction:

What to Look For

When selecting a stretch fabric for an underquilt, pay attention to these features:


Stretch fabrics come in a gazillion colors including solids, prints, metallics, florals, and yes, even camo.

Where to Buy

You can buy stretch fabrics from many places, but the one with the most selection that I found was Spandex World. You might look at:

Your local fabric store will also carry a limited selection of stretch fabrics. Black spandex and power mesh are easy to come by, but these are not ideal either.

I recommend you order two yards minimum. You need one yard for your project and some extra for practice and for mistakes.

Design Strategies

There are several fundamental design concepts you can work with. They all mix 3 basic ingredients: quilt body, extension fabric, and stretch fabric. Stretch fabric will in most cases be Stretch Mesh. The extension fabric can be any ultralight fabric such as Membrane fabric from Cheap polyester and nylon fabrics work fine too.

Gathered-End Cap

This is the simplest design. You just sew on a large section of stretch mesh to each end of the quilt body. The ends of the stretch mesh are rolled over and you sew a channel to put a drawstring though. The ends are gathered just like the ends of your hammock and attach to your hammock's suspension line or gather-knob.

Double Banded

This design puts a small band of stretch fabric on both sides of the quilt body and uses extension fabric to fill out the rest of the length. It works well with heavier spandex and power mesh fabrics because it doesn't use as much. It has less maximum stretch ability compared to the end-cap designs, so is better suited to building a quilt for a specific known hammock length.

Single Banded

This variation of the banded design uses one large band instead of two narrower ones. This means that you can hang the fixed end a fixed distance from the end of the hammock and get the same result on every hammock, regardless of size. If you are making a short quilt body, you might want this.

Triangle-Fan Cap

Triangle fan caps are an optimization of the gathered end caps. It's the same concept, but with half of the fabric removed, saving weight. The tradeoff is more sewing time and a somewhat less robust product. If you are using 2-way stretch fabric, you must keep the fabric aligned along the stretch axis. This means cutting out several triangles of fabric and stitching them all together into a conical shape. If you are using a static or 4-way stretch fabric, you can cut out a conical shape directly.

How Spandex Quilts Compare



The only noticeable drawback for a spandex quilt is the added weight of the extra fabric. This means that it may weigh 1-3 ounces more than a typical side-channel suspension that uses 1/8" shockcord. However, with a smart cut and ultralight fabrics, you can negate most of the extra weight. Even if you opt for the easy-to-make option that uses more fabric than necessary, some folks will gladly trade 2 ounces of weight for a guaranteed gap-free hang.

Underquilt Suspensions Compared

  Spandex Channel 4-Corner Wooki Clew
Suspension Weight 2.5-4.5 oz 2.5-3.0 oz 2.0 oz 2.0 oz 2.0 oz
Difficulty Average Average Easy One-Piece Fiddly
Center Tension Yes No No Form-Fit Yes
Side-Squeeze None High Medium None None
Hammock Swappable Yes Yes Yes Possible Yes
View Blocking No Yes Mild No No
Short Sizes Yes Yes Yes No No
No-Sew Options No Kinda Yes No Yes
Sit-In Proof Maybe Yes Maybe No Maybe

Special Suspension Notes

Construction Techniques

Sewing Supplies

Thread: You can use regular polyester thread for sewing spandex fabrics. Do not use cotton. This is good advice for just about any outdoor gear. Some guides on the internet recommend using naturally stretchy "whooly nylon" thread if regular polyester just isn't cutting it.

Needles: Ideally, use a stretch needle. Stretch needles are specifically designed to avoid skipped stitches when working with stretch fabrics. You can use a regular sewing needle but it might be fussy. Some guides recommend using a ballpoint needle. However, these are meant for knit fabrics and not spandex.

Sewing Technique

Use a zigzag stitch! This is the most important bit of advice. If you use a straight stitch, all of the stitches will pop when the fabric is stretched, while a zigzag stitch will merely straighten out like an accordion. Your machine may have additional stretchable stitch types, but regular ol' zigzag will do the trick. If your machine has a "lightning bolt stitch", use that. It's like an advanced zigzag meant for intensely stretchy stuff.

It is okay to use a straight stitch when sewing along the width of the fabric or when joining to non-stretch fabrics. The underquilt stretch is only going to be along the length. This means the hemmed edges of the stretch fabric sections must use a zigzag. Triangle fan seams will also require a zigzag.

You can use the normal presser foot when sewing.

Do not pull or push the fabric through the machine or it will pucker. Stretch fabrics are not slippery, so they should go through the machine without additional help. If you have any trouble, pin the fabric with toilet paper, tissue paper, tape, or newspaper. This provides a better grip going through the machine. Remove the paper when finished.

Fixing Floppy Sides with Convex Edges

All things being square, any of the above quilts concepts will have somewhat loose sides. Some people like this. If you want snug fitting sides, you need to shorten the total length of the quilt along the sides. This will cause the stretch fabric to pull tighter along the edges, making floppy sides go away. We can achieve this effect by simply cutting a convex curve along the stretch fabric before sewing it onto the blanket. Assuming you are doing this on both sides, a 1-2" cut is enough to fix floppy sides.

Making a Triangle Fan

A triangle fan creates an end cap with a reduced amount of fabric to save weight. Create a triangle fan by cutting out 5 (or more) triangular segments from stretch fabric. The stretch axis needs to be aligned with the length. If you miss that detail, your work is in vain.

After cutting, each segment is hemmed. Straight stitch hems are okay along the width (top and bottom edges in diagram). You must use a zigzag stitch along the lengthwise edges. This is where the stretching occurs. You can hem all sides of a segment in one pass on the sewing machine.

Each segment has the small end folded over to create a small channel to run a drawstring through. This is what binds them all together and hangs the quilt up.

Segments are sewn onto the short side of the blanket. A drawstring is fed through the channel on the end of each segment.

There is no need to sew the long edges of the segments together.

Making a Conic End Cap

A conic end cap is a single-piece alternative to the triangle fan if you are using 4-way stretch fabric (i.e. "regular black spandex") or solid non-stretch fabric. This is likely going to be heavier if cut from regular spandex, thus self-defeating, but presented here as a thought experiment. You can remix this idea with a double-banded stretch mesh design and ripstop nylon for the end caps.

Project Examples

I am not an expert seamster. If you have better sewing technique, please feel free to do your own thing here.

Gathered End-Cap Costco Down Throw ("Spandex CDT")

This is the design I used for my prototype quilt. It converts a Costco Down Throw blanket into Gathered End-Cap stretch underquilt. You will need one Double Black Diamond Down Throw sold at Costco or Bed Bath & Beyond, one yard of stretch mesh fabric, and optionally some extra fabric for making a drawstring collar. This example uses a separate material to create a drawstring channel on the ends. However, you can just as easily skip making a separate collar by putting the drawstring channel directly into the end of the stretch fabric. Your choice.

You can use this basic pattern to convert any kind of blanket into a pseudo-SnugFit underquilt, including cheap sleeping bags, bed spreads, Snugpak blankets, military poncho liners, etc.

Step 0: Prep Fabrics

Cut two 18x60" sections of stretch mesh fabric. Cut two sections of 5x60" collar fabric (any light nylon or polyester fabric is fine). Optionally rip out short seams on the Costco blanket to increase loft (strongly recommended).

Step 1: Hem Spandex

Roll the short edges of the stretch mesh over twice and hem with a medium zigzag stitch. Must be zigzag. Got it?

Step 2: Hem Collar Fabric.

Hem all four sides of the collar fabric by rolling the edges over twice and sewing a straight stitch.

Step 3: Attach Collars

Sew the 60" edges of the collar and mesh together. Turn over and sew the far edge of the collar onto the other side, creating a channel for a drawstring to slide through.

Step 4: Stitch to Blanket

Lay the mesh over the blanket and line up the 60" edge. Pin the mesh to the blanket and sew the 60" length about 1/2" from the edge.

Step 5: Fold and Stitch Blanket Seam

Fold the mesh over the seam you just stitched and stitch a second seam about 1/4" from the edge, trapping the rough edge of the mesh underneath.

Step 6: Add Drawstring

Take a length of cord (anything works) and pass it through the collar channel to use as a drawstring. Alternatively, install a fixed loop with a lark's head knot, very similar to a hammock.

Done! Go hang it up by tying it onto the hammock suspension with either a simple slip knot or tying both ends together like shoe laces. Hang it a bit loose to not squash the blanket flat.

Thanks for reading. Happy hammocking!