I'm sure this concept has come up but I couldn't find anything on it so here goes. I was laying in bed when the thought suddenly hit me heat rises correct so why don't I build a quilt with a thicker insulation on the top and sides going down to the pad. But for what gets stuffed under or almost under me most of the night why don't I use a thinner insulation? Then I took it another step even when sleeping In a down sweater up top, and just thrermals for my legs my upper body feels cold much before my lower. So from say knee leval down I could use a lighter insulation as well. I'm not a expert so would this work as well as I think it will? I guess it's kind of the same concept as wearing a vest not a jacket since your core needs more warmth. This quilt will be used for a xul/sul so I was going to make it with a closable head slit to be worn as a shawl.Second matter of thought was I still have the idea of usig tyvec 1443 as the outter shell since it's a great barrier at passing moisture and resisting water then I was going to use a 4.5mm silk as the inner. The insulation would be a combo of climashield apex 2.5 and 5 or maybe 2.5 and down hmmm. That would mean only about half the baffling for down and i could use 1443 for the footbox where the climashield is and 7d for where the down is?Last question is I have heard you lose some warmth going from something like m90 as a liner to silk is this true ? If so how much? So if you could answer the poll of questions to help me decide how to build this thing I would appreciate it especially input from Tim marshal te-wa javen and all you top notch quilt makers.

Variable insulation. Yes ? No ?
If yes with 2.5 and 5 ounce climashield or 2.5 and down?
If down how much loft of 900fp to match warmth of 5 ounce climasheild
Tyvec outer ?
If yes just foot box or full quilt ?
If just foot box m90 or 7d over the down section or upper section?
Thanks for reading all my wierd ideas if you can offer advice id be glad to hear
Silk or m90 liner?

I've been think about making a top bag with two layers of 2.5 over my torso and just one layer over my legs.

I've noticed that when I am pushing the temperature limits with my current bag, I get cold around my torso, so a second layer there would push my temperature limit down.

I'de have the entire length be 80 inches, with the torso double layer 40 inches. The insulation is 60 inches wide. Cut two pieces long enough to wrap around, which would be 46 inches for me. Cut one piece into a 40 inch and a 20 inch wide piece. Then I'de have no waste. There'd be a seam 20 inches from the top but it wouldn't matter because of the second layer.

Maybe something like that would work with a quilt.

That's basicsly what I was thinking Jerry but instead of double layering 2.5 I would use 2.5 and 5 just because I already have 5. But now I can't get the idea of a climashield/down quilt with a tyvec footbox out of my mind if it worked well it would be exactly what I'm looking for