This is a great quilt for those that sleep cold. The planning is, IMHO, the most important part of making a quilt like this.
I based the basic dimensions on cross between Nunatak's "back country blanket", and "dual arc alpinist. I planned on finished baffle height of 3 inches at 5.25 inch spacing, but there was enough over fill that it lofts a lot more than this. I figured on an inch seam allowances all around. I used 0.85oz/yd downproof nylon for the shell and lining, and nano-see um netting for the baffle material. The drawcords are aircore spectra 2. The down is 800+ fill power. All the materials (except the aircore) came from Thru_hiker.com
So initially there is quite a bit of maths involved in working out how much fabric and down you need, how you're going to cut it, etc...I cut the nylon with a soldering iron and straight edge ruler to prevent unravelling. Getting the tension right on the sewing machine also took some patience. The 'funnest' part was weighing and adding the down. I did this in a tent, inside the house, with some fine scales I borrowed from work. I also had a vacuum cleaner ready to go in the tent. More maths involve in how much down to put in each channel, given that the bag tapers from top to bottom so that each channel needed a different amount of down!
Then the tweaking began. The extra nylon flaps I originally added just didn't work as I mentioned. So I removed this and added the velcro tabs to both the quilt and our sleeping mats (two Stephenson's DAMs). At this stage I also added velcro to the bottom edge of the foot box so it would actually fold under the ends of our mats and form a draftless seal. We found that the velcro was under enough stress that it would partially rip whenever we moved, waking us with that lovely velccro sound. So then I removed that velcro and just went with the drawstring foot box. But this left a small hole where cold could still seep in, so I added the extra draft flap. This is a very warm foot box! The original top collar I used was like the one on the dual arc alpinist. We found this wasn't quite enough on really windy nights in a Tarptent. In fact, the draft flap in the footbox was originally the neck flap. I made a longer draft tube that covered most of the length of the top opening, and now we're happy. Just as well I had some spare fabric and down to work with. Actually, the spare fabric and down were meant for making a doggy quilt, so now I'll have to think of something else for poor pooch.
Overall a big project for me, and not dirt cheap either, but fully satisfying and just exactly what we want in a sleep system. It would have been hard to just order something like this even from the custom places like Nunatak and Feathered Friends as the design has continually evolved.