This is mostly just thinking out loud- I don't think that I'll be taking my kids camping in the snow this winter, but hopefully soon.
Here's my situation: Winter nights in the Sierra are typically in the teens (F), but drops to 0F are common and -10F sometimes happens.
I want to get out tent camping with my kids and possibly wife in the winter (instead of always using our heated trailer). We all have sleeping bags that are rated at 15-20 degrees. With their bags, my kids are comfortable sleeping at freezing in just light long sleeve shirts and shorts. To push the comfort temp down to zero I'm considering making one or two double overquilts.
We would use the double quilt in conjunction with a large foam pad such as SULUK 46 Plastazote 3/8" x 50" x 74", which weighs 13.2 ounces, or Volara foam which is heavier but cheaper. On top of that we would use our summer 1-1/2" self inflating pads. I imagine attaching the quilt to the pad with snaps, omni tape, etc at least for the lower few feet.
Paul Nanian (AYCE) suggests that 1 CLO is worth about 10 degrees. Using this number I want about 3 CLO to pull the kids' comfort zone down to zero. Climashield Combat is rated at 0.79 CLO/OSY. With a weight of 3.7 ounces/yard2 it provides 2.9 total CLO from the insulation. How much more from 1.1 ripstop shells and airspace between their bags and the quilt?
I think that would give us the edge that we need. If we use 1.1 OSY shell fabric the total weight becomes 5.9 ounces per square yard. Bumping the insulation to 5 ounce XP with clo/osy of .82 makes the insulation CLO 4.1 and weight 7.2 ounces per square yard. With a size of 84" long x 76" at the head tapering to 60" at the foot (before taking out seam allowances) it would be 4.4 square yards. Weight would be 26 ounces for the Combat or 32 for the 5 ounce XP. Add the ground sheet and the total is about 3 pounds for the Combat version.
How wide does one make a double quilt? Fabric and insulation are typically 60" wide, so keeping the maximum finished width at about 58" would be easiest, but too narrow for adults. It seems to go wider it would be simplest to run strips of fabric and insulation down the sides at 90 degrees to the insulation orientation in the main area. With three yards of shell, liner, and insulation I'd have plenty for an adult size quilt, with two yards of each it would be kid sized.
If this contraption would work for me and my 7 year old in the summer that would be handy too- which pushes me towards using the 5 ounce insulation (small cost increase, no labor change, 6 ounces weight, 10+ degrees temperature).