Jim and I have been using down double top-quilt for 25+ years. The first two were hacked rectangular sleeping bags. The one we currently use is a 10 year old custom Nunatak back-country blanket which I tweaked. I'm ready to build a new one that incorporates a few improvements, including lighter shell fabric.
I've got enough experience using double quilts to know what dimensions and features I want. I've done enough sewing to think I can do this without creating a total disaster, but not so much skill that I'm not nervous :)
I've been reading old threads about making quilts, and have gleaned a lot of useful information. Now I'd like advice. For reference, we sleep in a traditional double-walled tent in night-time temps ranging from 25 to 55.
First question... After reading all the threads I could find on fabric options, I'm planning to use M50 for the shell and Nobull (aka 8D, EightD) for the liner, as recommended by Aaron Sorensen in a recent thread. Is there a compelling reason to use a different combo? I fear that I may have missed threads discussing advantages and disadvantages.
Second question... I'm considering making the baffles run along the length instead of the width. The overall bag will be ~70" wide (tapering at the bottom) and ~77" long (plus foot-box and pleated neck flap); so there's not a big difference in the chamber length if I run the baffles in the non-standard direction. It occurs to me since width is so much shorter than length on a single-bag, the chamber size is smaller with horizontal baffles, and therefore down is more controlled by horizontal baffles. But a double-bag is not so dissimilar in the dimensions.
I think there might be two advantages to length-wise baffles, but I may be completely wrong, and I'd hate to find out after all the cost and labor of building the bag. First possible advantage is that there's not as much vertical relief along a chamber that runs head-to-toe as there is in a chamber that runs from floor over the body and down to the floor on the opposing side, so possibly less shifting of the down during the night. Second possible advantage is that it would make it very easy to build baffles for a differential cut, where the shell is a greater circumference than the liner. However, I'm not sure that a differential cut would actually be that useful in a top-quilt in the same way it is in a mummy bag. Eager to hear opinions.
Third question... I haven't seen MYOG designs that use trapezoidal chamber shape, and wonder if there would be an advantage.
That would add an ever so tiny bit more baffle material, but those two sites imply it gives a better result. It shouldn't be any more difficult to make it with trapezoidal chambers, so if it gives a higher quality result I can't think of a downside. Thoughts?
Thanks very much,