Hammock Underquilt Project Planning

[cwaskey]

I’m looking for input on an upcoming hammock down underquilt MYOG project. Below I’ve shared my thoughts on design and construction. Feel free to comment if you have thoughts on how to make it better. Although most of my gear is homemade, I have not worked with down before. This will be done at the same time that I make a down top quilt, which will be in a different post. I plan to post my finished results once I’ve completed the project.

a. General
I’m planning to sew a down underquilt in keeping with my ultralight style. This includes a minimum of extra weight, but enough insulation to keep safely comfortable since I won’t be carrying much else to use as backup if it gets cold. The weight of the underquilt needs to be comparable to my NeoAir Xlite air pad (12 oz.), which is what I’ve used until now. The reason I’m not happy with the pad in the hammock is because I typically sleep on my side, and the pad curls just a little too much for my back to be straight, even when used on the diagonal. In warm weather, I’ve taken naps on just the hammock fabric, and my back has been comfortable. Although I can get comfortable by lying on my back on the pad, I don’t generally sleep very well on my back.

The average January low temperature is 25F in my area. Although many nights in a given winter are below this average, I would like to target something that would work down to about 20F with long johns on. This would allow me to go out on virtually any night of the year, unless I get really unlucky with my scheduling.

b. Geometry
In many underquilt designs, I see that the head and foot ends are cinched up with shock cord, compressing the insulation in order to seal the ends to the hammock. I want to avoid compressing insulation that wasn’t needed in the first place. I plan to do this by removing a triangular wedge out of each end and sewing the sides back together. This results in a cupped shape, somewhat like an origami boat.
Underquilt outline.png

The top (outer) fabric will be sized larger than the inner/liner fabric, so that I can pull the liner tight against the hammock without compressing the down insulation. I will add darts and corner treatments to the outer fabric as necessary to achieve this.

I’m undecided on suspension. I like the triangle G-string style supports, because they pull the UQ both out and up, but I don’t typically use a ridgeline, so adding one would mean additional weight and setup time. I am afraid just pulling the corners of the UQ to the ends of the hammock would allow too large of an air gap at the ends. The UQ could be suspended by Velcro or snaps directly to the hammock. This would certainly prevent air gaps better than any shock cord suspension, but I’m not sure if putting holes in the hammock (such as for sewing the Velcro backing on) would weaken it and cause the fabric to rip under load. Attaching the UQ this way would also prevent me from switching sides without having to get out and re-attach the UQ to the opposite corners of the hammock.

I do plan to put shock cord in a channel at each end to be able to cinch the ends, but I’m hoping the geometry will minimize the need for this as much as possible.

c. Materials
I plan to use a breathable DWR material for the outer shell, while using the lightest down-proof material possible for the inner shell. Argon 67 and Momentum 50 are both contenders for the inner shell, and possibly the outer shell, though I may go to something a little heavier. I don’t want something on the outer shell that I’m going to have to baby.

d. Insulation/Baffling
There are many formulas and opinions about how much insulation would be required for 20F, but I’m thinking I will need about 2.5” of loft. I have a synthetic top quilt with about 1.8” of loft that I have used comfortably on the ground with insulated clothing down to about 20F.

In order to provide an overstuff, which will hopefully reduce the amount of down shifting, and makes the UQ look really nice (I think), I will plan on 1.75” high baffles and a 2.5” total loft. I plan to use 800 FP down, approximately 8 ounces. I plan to orient the baffles lengthwise, to further reduce the risk of cold spots due to the down shifting.

Because the underquilt is tapered, the longitudinal baffles will be a bit tricky. I may either use straight baffle chambers that begin and end on the tapered edges, or I may create baffles that are farther apart near the center, so all baffles begin and end on the ends of the underquilt.

[jjr]

Your plans look a bit too narrow to me. I would imagine 40 inches minimum at the shoulder. I made my UQ pretty much just like the one in this thread [link] https://www.hammockforums.net/forum/...shaped-baffles [/link]. The darts made a nice tapered shape and I really don't have to snug up the shockcord much on the ends. My next one I am going to make the same but 43 inches wide inner shell and straight baffles. I used 9 oz of 850 fp down for my 3/4 length UQ and it is def good to 20 Fahrenheit, prob 15, but the lowest I've slept in it was mid 20s.

[hutzelbein]

I haven't made an underquilt myself, yet, but HammockGear underquilts are cut similar to this pattern: https://www.hammockforums.net/forum/...h-fitted-shell

[cwaskey]

Forgive my lengthy delay in posting the finished product. Things have been a bit busy at my house, including baby #7 being born this year.

I finished this back in April, shortly after finishing my top quilt, but due to a lack of cold weather, I have not had a chance to test it below about 50F since then. In that temperature range, it is more than adequate and very toasty. I used the remaining down from the 2 lbs of 800fp a friend and I bought to make top quilts and this underquilt; about 8 oz. remained, I didn't measure it. The UQ is a good 3" thick, maybe more, which is better than I planned on. Including the shockcord and mitten hooks that I use for the suspension, the total weight of the UQ is just over 13 oz.

I ended up making it a little wider based on feedback here, but kept the tapered shape. I added shockcord draw strings to each end, so I can draw the underquilt tight to the hammock at the ends. I decided to go with a karo-step baffle design, and it turned out to be a lot easier than I expected. It also makes it very easy to get the down where I want it. If I want to shift the down around, I just hold the UQ with one hand and beat it with the other until I'm satisfied with the down distribution. The baffles are on a 12" grid, with each baffle 6" long, and one row of baffles on the centerline of the quilt. Below is a sample of my baffle pattern; it does not show all of the baffles, but should give you an idea of how to lay them out.

quilt baffle layout.png

The fabric shell was made similar to my topquilt, with excess material planned into the outside shell, so I can pull on the edges without compressing the down.

Underquilt shell.png

I believe the quilt turned out nicely, with a few issues that I have not yet resolved. First is that while the quilt fits nicely to the longitudinal hammock, it tends to slip out from under my head and feet when I lie on an aggressive diagonal. I've looked at pictures of commercial underquilts and noticed that almost all of the pictures with someone in the hammock show the person lying straight. My guess is that all underquilts suffer from this, and the suspension has to be fussed with to get it to stay for someone actually on a diagonal. I have not tried triangles yet, but that may help some.

The second issue is that because my design is wider in the middle than at the ends, there is nothing actually holding the edges up. In warmer temperatures, this is not an issue, but on colder nights, I solved this by crossing shockcord over top of me to hold the edges together. This makes getting out in the middle of the night a little more complicated, but it also helps to hold my topquilt in and makes for a very toasty cocoon.

The overall length of the UQ is about 60", which was planned to provide a 3/4 length quilt. Although this less than my height, it actually does stretch over my whole length if I lie on my side on a diagonal and bend my knees a little. At least it does as long as the suspension doesn't slip off my feet or head (see above). As you can see below, the length is more than enough to cover my 8 year-old son when he lies completely straight.

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Thanks for the tips that helped my make this project better. I hope what I have shared here will help someone else in the future.