I like Cashs mom's idea. Make a pieced duvet cover for your comforter. My sister has done that for her grandkids. And in summer, the comforter comes out and the pieced duvet cover is used as a light blanket on their beds. And just think, you could make the 'front' and 'back' in two different patterns so it would be reversible!

Oooooh! I never thought of that! Great idea!

My family traditions are much more along the down comforter with duvet/cover than quilting. So while I did grow up knowing how to take care of down, we didn't have any quilters in the family until me. If the cover was fancy, it might have some (usually) blue embroidery.

Turns out, although I wasn't diagnosed until my 30s, that I am allergic to down and that maybe growing up in Alaska when I did with down jackets and down house booties and down everything wasn't such a great thing. I remember describing sleeping under the down comforters as "prickly" but was told I was just being picky... That's ok I was happy with the pink acrylic blanket instead of the prickles. Still no down pillows for me, doc told me to not keep birds in the house or even have a chicken coop but I'm fine with eggs.

Anyway, I second the idea making an envelope from at least one pieced top if not too, No batting, just a backing to keep all the seams nice and you can even do a bit of quilt design if you want.

Turns out, our children really are asking for help when they don't understand what's happening to them. My daughter was lactose intollerant. The symptoms aren't pretty or socially acceptible. Took me awhile, but finally figured out what was wrong (I'm a dietitian with lots of knowledge and still it took me awhile). The teachers and cafeteria were thrilled to work with us to make sure she stayed on her diet.

Peckish,
No, if you make a front & back and slip the down comforter inside, it doesn't mash the down at all. Hotels that have down comforters use a duvet also because you are able to keep the comforter clean longer by washing the cover when necessary. We also have a thick flannel duvet on one down comforter and it works out perfectly:)

You've already got a bunch of really great suggestions about options for getting the beauty of a pieced quilt top while still keeping all the warmth, but I want to add my comments on the original question. When comes to insulation: warmth = thickness of insulation (assuming that the insulation is not so loose in its construction that the heat easily escapes, e.g. dry leaves not in a sack). I read of someone setting out to do a scientific study of different sleeping bag materials and the insulation they provide. They quickly discovered that it was just a matter of thickness; with the same type of construction a 3" thick down-filled sleeping bag provides the same amount of warmth as a 3" thick polyester-filled sleeping bag. For backpackers, weight and compressiblility are big considerations, so the down's light weight and ability to squished small are very appealing, even though it costs more than synthetic fills.

This all means that a very light quilt *might* not change the insulation/warmth. If you want to test it, the easiest way is to measure thickness is to spread out the comforter on hard floor and gently drop a meter/yard stick onto it so that it is level and sticking a little bit off one side of the comforter. Measure the distance between the floor and the stick. Take off the measuring stick and put the quilt on top of the comforter, and then repeat the measuring process. If the second measurement is greater than the first, then the quilt has increased the warmth of the setup.

Cindy, the hiking nerd and gear weenie, who sometimes quilts
AKA platyhiker

Just reading your post about allergic to down. I have a wool duvet. It's actually 2 duvets snapped together spring/fall + summer and snapped together it's a winter duvet. I have down duvets as well but this is the warmest and most versatile duvet. It's made by Daniadown.