I second Rog's compliments on your quilt. I was impressed when I saw it.
I found an old photo of a summer sleeping bag (with me in it) that I made using the row cover about four years ago. It was four layers (outside --> inside): aluminized PE (like heatsheets), 0.3 oz row cover, aluminized PE, and another layer of row cover on the inside, against my skin (it's soft). It was fragile but warm (even through some frost and light snow one night on a grass pile without a pad), and it rolled up to about the size of a heineken can.
Polypropylene has both the lowest density and the lowest solid thermal conductivity of any textile fiber, and it's water absorbtion is essentially zero (a little less than polyester and a lot less than nylon). Also, the very tiny fibers in spunbonded polypropylene (less than 1 denier) make for a lot of tiny air spaces, and excellent insulation for the weight. Tensile strength is poor, though, and I've found that it has to be replaced about every year.