an order of magnitude (at least) more body heat is lost by conduction and convection than by radiation, and a mylar film would add a couple more ounces, so I'll make the prototype without, and then try putting a reflective film over to see how much difference it makes compared to an extra layer of light air filled poly. An important part of the aim is to make this as condensation free as possible. Also, as Andrew points out, mylar film is noisy, though the silvered heat sheets made by adventure medical aren't. I just got a new one of those through the post and I may sacrifice it to the experiment. Putting the film in the middle of the quilt with a layer of row cover will help damp noise.
Huzefa, we don't know until we try, and it won't cost much to find out. I can't afford a cuben/down quilt. And I like the idea of a quilt which would roll up and fit in my pocket. :o)
If it works well, I'll consider spending some money on some cuben to shell it with. I anticipate that putting some effort into shaping will be important, as will the size, number and placement of vent holes.
Kevin, are you talking about bubble wrap, or something else? Expanded polythene sounds interesting, but being able to expel the air and wrap this small is part of the aim.
Work begins tomorrow.