I'm not sure what they're called, as I tossed the bag they came in, but I'm using these little silicone bands the girls are using to make bracelets. I guess the bracelets are a big thing now, and the bands are in Wal mart, Walgreens, places like that. My bag has 5 or 6 different colors. I had to stretch them pretty good to get them on over the foot, but they're a perfect size for my large fowl ladies. They're fairly small diameter, so I used 2 bands of the same color to make it easier to spot in the flock.
I've only used these a little over a month, so no claims to durability.....