They're 100% manmade materials, "microsuede" and such, so they're not actually leather or sheep's wool fleece, but at $15 I'm not going to complain.
I picked up the Size 10-11 pair on Friday, and trying them on when I got home and cut the tape on the box, discovered they were too small. (Most of my shoes are 10.5.) I stopped in again yesterday afternoon, and they gladly let me swap for the Size 12-13 ones. (Even those are snug.) Amusingly, the ones I returned still had the little plastic thread holding the slippers together, and the replacement pair did not. Someone must've tried those on, too!
When you go to buy yours, try them on or assume you need a bigger size than you think you do!
After buying these, I went to riteaid.com and entered all my receipts for the promotional period that ended on October 17th. If you spent over $100 in that several weeks, they'll send you a $20 gift card, and if you spent less, there are correspondingly smaller kickbacks.