That fabric looks like what we here in Australia call unbleached calico. I think its the same as unbleached muslin to you. There is a similar fabric here that we call homespun that is a more refined cotton, but going by the vintage of the quilt, I'd say it is calico.

Love the quilt top, it is just gorgeous.

there are many weights of muslins- just because it is heavier than what you've experienced doesn't mean thats not what it is- but it could be feedsack's too - either way it's a muslin
backing it with a nice quality muslin would be nice- you could use white or natural
the fabrics are vintage 30's-40's fabrics
if you wanted to use a print for the backing instead of a solid-or muslin you could pick up a repo 30's fabric that goes nicely with it-
connecting threads have some nice ones for very reasonable prices.
great find- can't wait to see pics of it finished :)

Thanks for all the compliments. I bought it on ebay from a lady who found it in her grandmother's attic. It was DIRTY! but it is gorgeous to me, even stained. Y'all have confirmed for me that the backing for the stars is probably some sort of muslin or milk/feed/sack. I've got a bid on an old muslin featherbed cover on ebay, which looks VERY similar to what I have here. If I win the auction, I think I will cut it open/apart to use for this quilt.

I have some of that white fabric that I had identified as 1950s. I am making a"bunch of snowmen" quilt as it is nice and fluffy like a snowman should be. I was thinking that either me or someone I know had a blouse made out of it and that sort of dates me. I understood than muslin was always flat where this has some texture to it.

WOnderful quilt, I think it looks like muslin.

I also think it maybe is flour sack material. Beautifule quilt....brings back memories of Grandma's stories.

Thanks! I really love it too. The stars are just perfect. I can't wait to play with it.

I don't have an answer for you but love the fabric and colors. Whatever you come up with it will be a precious quilt.

Well, I bought some backing fabric and binding fabric that I think will pull out the shades I like the most. I'm excited to put it together and see how it comes out. I'll post photos ;)

Looks like feed sack cloth, dress cloth and muslin. Remember muslin that is 100% cotton unbleached seems thicker and of course is rough. It is really a nice piece, I would back it in muslin also. Maybe take it to your local quilt shop they should be able to offer you some ideas. Good Luck