I have spent the last day and a half making my new summer under quilt. Thru Hiker M50 (Aegean Blue, which is not as dark as I was hoping) and 4.5oz of a stash of Wilderness Logics 850 down.
I roughly used this thread as a basis: Summer weight, sewn thru under quilt - instructions
There are 9 channels each with .5oz of ~850 down in each.
My inner piece of fabric is 43.5"x54" with markings for the channels every 4.5". Each marking was then darted 17" down and .5" wide.
The outer piece of fabric is 59"x54" with markings for the channels every 6.25". Each marking was then darted 17" down and 1" wide.
I used 3/32 shock cord for gathering the ends and for the suspension (which is tied to the ends and does not run down side channels).
Weight is 313g/11.05oz, which is more than I was planning on (I was hoping to be under 10oz). I guess I'll have to try again some time.