My kids had lots of fun with these rollers. They are a plastic with a picture on top and metal ball bearing on the underside. As usual there is a set to collect, and of course you get two random ones in the pack. My kids are not collecting the set but just had fun creating their own games and setting targets as to how far they could roll. I personally bought them to round off my purchases to achieve supersaver delivery and gave them away as a small reward treat. A fun little item to suit any doctor who fanatic.