Is it cotton.
 

I bought packs of sqaures sold as “moda 100% cotton from a reputable vendor. The card lists. All the moda numbers to match. Buuuuut some feel like a non-cotton. I ripped one to see if cotton but find myself wondering if maybe can be cotton. Ever bought moda before. Do some of their cottons look like non but really are.

If you suspect it is polyester, you can try ironing it. Generally polyester has a chemical smell when ironed. But cottons can be woven with a variety of "feels". I am surprised that the fabric doesn't feel the same if they are all from one grouping.
Just as an aside, most brightly colored Kaffe Fassett I have used feels very fine, almost too limp to use with regular cotton.

You can also burn a small piece of the fabric. Cotton smells like hay or grass burning and looks like a piece of burned paper. If there is any manmade material, it will burn with a chemical smell and the ashes burn into a small hard lump. The more manmade, the larger/harder the lump in the ashes.

Here's a handy burn test chart:
http://www.fabricmartfabrics.com/Burn-Test-Chart.html

Thank you for the help. You all are fantastic! I did a burn test and it IS cotton even though it seems more like “windbreaker” material feel. Thank you.

Great chart - thank you for the link.

Yes, thank you for that link! I have it saved to my favorites. I could distinguish between cotton and "not" cotton, but this is much more detailed.

Thank you so much for this! I have a couple pieces of fabric that I can't tell, one is a lovely Asian fabric that doesn't have anything on the selvedge and I am afraid to use it in a quilt; the other seems to be cotton, but it feels like it is starched even after washing, this last one I picked up in a thrift store, it was so pretty, dark navy blue with small red flowers. that I couldn't resist it. I will try the burn test on these, thanks to you, Paper Princess!