I am making a new underquilt from an old sleeping bag. I have no idea what the rating of the bag was but I would guess in the 40-50° range. I am considering rigging a space blanket to help extend the comfort range of my system.

My first question is exactly where do I place the space blanket. I have read the sticky vapor barrier thoughts thread, and but I missed the point of where is the most efficient place to put this.

Second, what is the best way to attach this? My SBSBUQ (SkeeterBeeterSleepingBagUnderQuilt) is being stitched in a spoon/bowl shape, rather than flat. It will have drawstrings on it.

Third, how much will this likely extend the comfort range of the UQ. I expect (hope) the SBSBUQ without the space blanket to be good to maybe 50° or so.

Last, what else can I do to extend the comfort range of the UQ? Would layering a small down blanket inside help, especially if it had the same "cut" as the SBSBUQ?

I will post more on this in the DIY section as I complete my project or run into snags which I need assistance overcoming.