Do you ever
 

I was ‘gifted’ scraps/ yardage from a deceased quilter’s family. Not all are cotton however. I can see the quilter cut pieces from the poly/cotton or permapress. Do you ever mix other fiber contents like this, with your cotton pieces?

I have used different fiber fabrics together, it just depends on what I'm trying to achieve. If the fabric is flimsy, rough, or just outdated, I will take it to my guild were one of our members used them for stuffing for animal pillows that she then donates to the local pound.

I made an interesting Crazy Quilt will all kinds of fabrics and blends. The quilt came out great! There are good places for mixed fabrics in some quilts.

Yes, I do.

I don't mind a whole project from non-cotton fabrics, but I won't mix them, just too many unknowns about if they would "play nice" together

I never have but I don't think there's any law that says you can't. :)
I'm always concerned about the integrity of the fabrics. With all cotton you pretty much know how they will behave.

I used cotton and poly/cotton (wash & wear) years ago. My late Son had one from many years ago. The poly/cotton was still there along with the poly batting I used. The cotton was totally gone. The quilt was made before I knew much about quilting.

I still have some poly/cotton I plan to use for my donation quilts. Just don't know when.

I prefer working with cotton but that was mostly learned. Starting in the 70s as I did (and earlier), the magazines at the time had a lot of positive things to say about using poly cotton fabrics. The durability, the colors, the sharp printing, the lack of ironing, all were positives. My biggest negative is that they are slippery and treacherous!

I will still use poly blends in "use" quilts, those meant to be taken in the car and used for picnics, or wrapped around a child who somehow got wet, or whatever needs you might have. I have a large funky piece of border print that I just love and I'm going to use it to back a scrap quilt that I am keeping for me. It may or may not last 10-20 years, can always put on a new back later if the top is worth it, but that's not a show top either.

For the last 20 or so years most of the fabric I buy is from estate sales or thrift stores with no labels. I've gotten really good at burn testing fabric. Nowadays there are videos but it is pretty easy to learn. Burn a piece of what you know to be quilting cotton. It should be fairly hard to light, not smoke, and leave a soft edge with maybe a little grey ash. Now burn something that is poly of some amount/type. First, be careful because it with light quickly and can burn brightly. t will smell like burnt plastic. It will have a hard edge, maybe with little pills of melted stuff. Smoke will be black. Wool and silk fibers will smell like burnt hair.

There are some rayons (made from plant fibers) that feel and burn surprisingly well and if they otherwise pass my tests I will use them despite my suspicions. I have one top that I made from actual scraps including clothing, and had a piece from a favorite rayon sundress that got a large stain. That used rayon lasted better than some of the fabrics I bought new in the top!

I never have for the fact that some fabrics may shrink or stretch where the other fabrics will not. Only in crazy quilts have I seen different fabrics used.