Thank you to all who responded. I am going to search around and find some premium muslin, hopefully local, but I will order online if I have to. My LAQ is fine with muslin as a backing.

Of course you can use muslin, but know that every stitch shows on the back of the quilt. I mostly use prints on the back of the quilt, so it hides the stitches, the starts and stops. And it doesn't show the wear as fast. If you do beautiful quilting, then maybe you want your stitches to show, and muslin or another solid color would be a good back for you. I don't recommend sheets due to the high thread count.

I have used the 108 and 120" wide Kona with good results. Be sure to prewash it because it does shrink a lot.

I like Southern Bell muslin, its high quality and only around $5 a yard. I bought mine at the independent local quilt store, not a chain store. You could do a search. I have whole quilts made with it so it does really well

I use muslin all the time. Sometimes bleached (white) and sometimes the regular old off white color. Love them both and often purchase it in 90" wide. Look for the better quality. I have searched JoAnn's and found some that is much better than others. When I find the good quality if have been known to by the whole bolt. Just as in any fabric there are variations in quality. Not all muslin is thin and see-through. In fact most is not!

I love muslin. WalMart has a Super Heavy Muslin for $3.97 which I love for hand embroidery. Muslin was used in the quilts my grandmother and aunts made and I use it extensively because I love the look and feel of a good muslin and when I can get the Super Heavy at WalMart for $3.97 a yard, I buy five to ten yards at a time.

Are you thinking of using muslin to save money? Or because you think the back of quilt should be plain? A king size quilt is a great accomplishment, and it should be celebrated with a fun backing. That way, it's almost as if you have two quilts in one. There is nothing that says the back should all be the same, plain fabric - not even the same printed fabric. I started piecing the backs of my quilts - mostly just in large fat quarter sized chunks that coordinate with the front - but they don't have to. Yes, it's a bit more work, but when you pull that quilt up and can see the fun underside, you'll be glad you did it.

I have not used muslin, but I have purchased sheets when they show up in the clearance section.

Tjere's nothing wrong with using muslin for quilting, that's what they used to use all the time. The quality varies depending on the thread count, you can shop around or else you can also use sheets.

I've just started quilting and find a lot of things can be confusing if your starting in the UK and reading posts from the US!

I am doing my first block swap with the US and the instructions said to use unbleached muslin for part of the block - which was a bit daunting as muslin to me is very thin and certainly wouldn't be something I used out of choice - then I did a little research and come up with some translations of the differences between US and UK terminology.

Muslin(US) = Calico(UK)
Calico(US) = Printed Cotton(UK)
Cheese cloth(US) = Muslin(UK)

Back to the question - I agree you can get some great all cotton sheets that look to be about the right weight - I have seen some in Asda in UK - which is owned by Walmart so maybe you also have them in US?