You can use anything you want - it's your quilt. But most of us use all one fiber, usually cotton, because of the way it handles, launders, and holds it's color for generations. It is sort of a quilting standard. Some also use wool. Use anything you'd like and see how it goes but I don't recommend mixing fibers.

When I have a fabric of questionable fiber content, I launder it -sometimes several times, and see how it comes out. If it holds up well, I use it.
Karlene

I am here to learn from those who have gone before me, made mistakes and learned from them. I think I will take the rayon out, they are dark colors. Several of the pieces came from my closet and have held up great. My concern now is their losing their color over the years.

Even cotton can lose it's color over the years if it's exposed to light etc.

I have a poly quilt top that has flannel for the backing and was hand quilted with BIG stitches.

It was left at my house during a hurricane and I never could find the owner.

This quilt has been used and washed a lot over the 15+ years I have had it and is still looking good!

I prefer the look and feel of cotton, but my Hawaiian applique book recommends a poly blend - I have never tried Rayon.

The problem with many rayon fabrics is ravel possibility. Our church quilt group has used rayon fabric and found this to be the case. If a quilt is washed that contains rayon fabric, it will be the rayon fabric seams that ravel out. We use 1/4" seams which leaves little room for fabric to ravel and seam to still hold.

Krissie

I have a quilt made by my great aunt in the late 50's or early 60's. It's a mix of 2.5" squares in cotton, rayon and every blend you can imagine that was in use in those decades. The cotton has worn just fine, but the rayon and other synthetic blends have come apart at the seams and in some cases just worn through.