I made a batik quilt (which seems to make the quilt heavier), put a layer of flannel in between the top and the wool batting, and then used flannel for the backing. It is very heavy and so, so warm. I did manage to quilt it on my DSM.

I think fleece would be very warm, but lightweight. I put one òn the back of a quilt for my DGD, she wanted it very warm for football games. It also had a layer of W&N. She played in the band.

when i want to sleep under heavy, I sleep under two quilts....whoa, that will do it.

My first thought is to suggest making a traditional Cathedral Windows quilt - not a "quick" or "easy" version. The traditional method gives you many layers of cotton fabric. To make mine extra-warm, I added batting behind the centers of the blocks. Perhaps because this is a quilt-as-you-go pattern, it never was a problem on my DSM.

Another idea is to use denim in your quilt. You can usually buy blue jeans made of fairly heavy denim at thrift stores (Goodwill, et al.) for very little $. There are lots of patterns/ideas on the internet for "jean quilts." I'm about to start making a rag quilt that combines denim and flannel for the daughter who has requested a heavy quilt. I'm still trying to decide if I'll add batting - but it seems like overkill. (Of course, it's July. I'll probably feel differently in January.) Don't know yet how my DSM will feel about the denim/flannel combo.

Of course, a Cathedral Window quilt - even a quick one - would probably be heavy if made with denim.

I recently made my daughter's quilt with flannel on the front and back, plus used Warm and Plush in it and boy is it wonderfully thick and cozy. I'm always stealing it from her when she's not playing with it (she's 18 months) but she loves to run by for a quick petting when Mommy's under it because she likes it too.

I, too, like a heavy quilt. I guess from that time we got iced in with no electricity for 3 days, learned a lot!! LOL But layering as many quilts as possible, we survived, now I prefer a heavier quilt. I made one for a cousin, flannel front and back with wool batting, too heavy for the whole bed, his wife said, but he uses it over his legs in addition to their regular bedding. He has trouble with his circulation and he says he stays warm. 9 patch and snowball.
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Regarding using denim for a quilt. I made a denim quilt out of old jeans. The pattern I used, sorry don't know the exact name of it, you 2 round circles: one made of denim and the other made of fabric. You sew the circles together to make a square. The round edges are sewn down and when you are finished it looks fake cathedral windows pattern. There is no batting in this quilt.

The moral of the story is this, even though the quilt turned out quite heavy, it doesn't seem to have the warmth you would think you would have. So, heavier doesn't make it warmer.

The heaviest quilt I've made was a t-shirt quilt. Another heavy one was the denim tumbler quilt (50 tumblers of denim and 50 tumblers of quilting cotton). Concerning your question, I would think that any blanket (even an old used blanket) would be heavy once sandwiched and quilted.

AZ Jane, I love your design!

I could tell you what I did once, but I don't necessarily recommend it. When I first started quilting, my daughter wanted a play blanket, so I took a cheater panel, backed it with cotton fabric, and in the middle I used 2 (yes two) layers of an old mattress cover from out king size bed, plus at least one layer of poly batting. God bless my old Kenmore, who managed to sew through all those layers, even if it was in a grid pattern to outline the blocks in the cheater panel, and she hardly hesitated at all those layers. My daughter would take it outside, put it on the ground and no rocks, twigs or whatever managed to come through that blanket and it was perfect for her Barbie dolls. I wonder what happened to it? LOL