My first major piece of DIY gear...
1.1oz ripstop seconds and noseeum baffles from Backwoods Daydreamer
800 fp Down from Hammock Gear
Here is a photo of the materials laid out, with the top and bottom layers overlapping. The baffles are about 9cm wide, including seam allowance. The top layer is 44" wide, plus 3" on each side for channels. For the bottom layer I worked out the width assuming the two layers form concentric semi-circles 2.5" apart. Then I increased the number slightly to work out to 1 extra inch per compartment, making 53". Then I added 2.5" on to each side for the outside compartments and another 3" on each side for channels.
This photo shows how I ruled the lines for sewing the baffles, because I needed something more visible than ripstop lines. First I marked the edges, then pinned each point along the edge of a flat piece of cardboard. Then I run a piece of tailor's chalk between the two points and a line is left along the edge of the cardboard.
I sewed small darts between the baffles. I then sewed much larger darts into the bottom layer to make the edges match up in width. The first baffle is also sewn to the top layer in this photo.
I calculated about 8.2 oz total of down. Since there were 9 compartments, I decided to just use 9 ounce of down to give a bit of overstuff. I got the down from Hammock Gear, pre-packaged into 1 oz bags, so it was quick and easy to just empty a single bag into each compartment.
I sewed 3 gross grain loops to each side in case any part needed pulling tighter.
This is a close-up of the channel end with one of the loops.
About 3" maximum loft
Set up for the first time on my Hennessy Expedition Zip (had to get Buster in the photo!).
You can see in the previous photo the large gap at the head end. I used a mitten clip to join the two edges over the hammock ridgeline, getting rid of the gap.
Comparing the underquilt with stuffsack to the Thermarest Prolite Plus. The Thermarest comes in at 750 g while the underquilt is about 506 g.