Loc: St. Louis, Missouri
Primaloft is a great synthetic insulation and you are talking about nearly 6 osy. I would think that thickness would get you down into the low 20s, maybe even lower. (Depends on whether you are talking about Primaloft Sport or Primaloft One).
However I wouldn't use Primaloft for a sleeping bag or quilt. For large panel projects like that you really want a continuous filament insulation like Climashield or Polarguard Delta. Primaloft needs a scrim layer to stabilize it and that weight penalty can be pretty big for a large panel item like a quilt. For smaller projects like jackets I hear that Primaloft is good (I've never made an insulated jacket myself). In fact you might want to ask if the weight you are stating includes the weight of the scrim. That would make a difference.
You might want to check out what they say over at Thru-hiker
Anyway, it's got a lot of loft. I got rid of the scrim, and found a (hopefully)good distance between stiches (about 7 in). This thing is reasonably light, but springs back to loft like a jack-in-the-box when compressed!
I'm curious to know about the temp rating. Please let me know - either here or a PM. I've been considering insulation for a hammock and am trying to keep my mind open to ideas before I start getting into it. This is one insulation that I investigated.
Time for a backyard test!
I always forget and make it more complicated than it needs to be...it's just walking.
I stitched first the lining with Primalof, then took the scrim off. Cutting (very carefully) along the stitches, or tearing, the scrim came off easily. I also made this quilt blanket-like, with a cinching cord at the foot and some velcro to keep some kind of footbox closed: the lower part of the sides can be assembled, like a "normal" quilt.
Loc: St. Louis, Missouri
I made a quilt out of climashield 5 oz. It was ridiculously easy. Lay the two layers of material on top of each other and then lay the climashield on top of that. Now sew around three edges of the quilt, trim any excess (mostly if the insulation is sticking way out), and turn the thing inside out so the climashield is sandwiched between the layers of material. Then sew up the top. Add quilting loops if you so desire (probably a good idea). Viola!
It's a little more complicated than this because you'll want some way of making a footbox. The easiest thing is to just put velcro or ties or something on one end. Or you could sew the footbox in permanently after the quilt is done. That part is up to your own creativity.