There are many different substances in plastics and pvc that can be potentially harmful.
This company has been producing safe products for children for more than 20 years. There are no harmful phthalates etc in these polypropylene play cups.
There are 8 cups in 4 different colors, all of which stack inside each other for baby to play with. They each have drain holes, so they are for play only, but perfect in the bath.
Available from Amazon.com