Sheet are great for tied quilts and I'm sure for machine quilting. They last forever! Made a tied bed spread out of sheets in 1980 and though it is not on top anymore, it is still going strong after constant use.

My mother in law has used sheets on the back of her quilts for as long as I can remember. She is now 93 years old and is still hand quilting. So you can use sheets on the back of your quilt and still hand quilt but she always says wash them first and don't get a sheet that has more then a 250 thread count.

I've used sheets for backings. As far as I know they haven't been a problem for my LAQ and everyone who has such a quilt seems to like it just fine. I love the availability of single size backings and the colors/designs are great.

I use new and old sheets. As long as the thread count is about 200 to 250 and no higher than that there should not be a problem with using them.

The only thing I'd worry about with used cotton sheets is rot from exposure to body oils. There is something about my DH's body chemistry - our fitted sheets become rotted and fragile on his side of the bed after just a few years and eventually start literally falling apart in the middle. I don't see the problem as much on top sheets but it makes me not want to use our old sheets for quilting, other than maybe for foundation piecing.

But new sheets - I don't see any reason at all why they wouldn't work. Just watch out for cheap poly blends that might pill up with use.

I use sheets as quilt backs all the time. And I mean all the time ! I have not had any problem with them at all. I posted a picture of my Waverly Sheet Quilt about a week ago and it was all sheets, front and back. I have taken several of my quilts to my long armer Marie and she has never said one word against it, I asked her after hearing negative comments on the board. I know they say the thread count is too high, but why does it work so well for me ? I would say to try it first on one sheet and see what you think. My Bernina sails right through it with no problem at all. I do use good needles and change them often.

I just used an old white sheet that was my grandmothers on a donation quilt for Oklahoma. I have a small box in the basement with these sheets. They are all pre-70's so are cotton. Went thru my Aunt's linen closet after she passed and added a couple extras.
They are no different than fabric for machine quilting...

Back in the 70's. My first quilt i backed with a sheet. My daughter loved the feel of the sheet her skin on those night she just wanted her quilt. I tried it with yarn. She had it on her bed everyday until the top came apart in the 90's. She took it with her to Rick's collage. It really pleased me that she loved that quilt as much as she did. Last year i went to bb&b got fannel sheets on clearance. Made the quilt using the flat sheet for the back. Then gave my quilt and the fitted sheet as a gift. They loved it. So go for any idea you have. You have nothing to loose.

I have used sheets for backs and have cut them up to use in various ways as I make a quilt top, however, I always tie these as they are not always needle friendly when you try to hand quilt them.

I have used sheets also. Often the local thrift store will have new sheets in the package really cheap. (save money for fabric!)