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.
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