I thought using a black polyester/cotton blend would be fine with 100% cotton. Then after I'd pieced and pressed a few blocks I noticed the black sashing looked way too short. Thought it was my cutting, so cut some more 9 1/2" strips. pressed them with steam on the usual cotton setting and they became 9 1/4" ! Lost 1/4" on that short strip!
My fault that I didn't know about using different temps but I was told mixing the two fabrics was alright! *sigh*
No polyester for me again!