Back in the 60's for a home ec project I used what I think was a poly/cotton blend as sashing on quilt squares (made by my mom and her sister for their hope chests) of 30's muslin crayoned and embroidered in the state flowers pattern. The 30's muslin started deteriorating by the early 90's, but we still got 30 years of constant use out of that quilt!
Use those poly/cotton blends...they will do wonderfully well in a quilt.

Heck .. in the 70's it was all the rage to make quilts using those polyester knits aka crimplene! Weighed a tonne!
So cotton with a bit of poly, why not?

Ok, I'll weigh in on this. I began quilting in the 60s and in ND we used most anything at hand. At least the quilters I knew. We did not do quilts for show, except for 4H.

I agree, I make quilts to be used and loved, not just hang around. My aunt has a wonderful stash of fabric of all varieties and we used them especially for charity quilts as this allows us to make more instead of having to be so frugal in this day and age. I have a quilt that she made for me 12-15yrs ago from knits and it still looks as good today as it did the day she gave it to me and is very warm indeed.

They will make wonderful quilts. My friend's mother and her quilting friends used gobs of shirting remnants from a shirt factory in their town. Quilts were beautiful. I agree with raptureready--If you are making an heirloom quilt, used 100% cotton, but otherwise, use what you have access to.