Please note that this section contains my personal notes from my readings on this topic.
Personally, I try to use stainless steel sippy cups (such as those by Klean Kanteen and Foogo). Glass has been around a long time and I haven’t yet heard of anything potentially harmful with glass. I’m still not comfortable that safer plastic alternatives are much safer than traditional plastic — they are just different. They are still made of chemicals that we hasn’t been full studied. If you’re uncomfortable with glass, however, below are notes from The Toxic Sandbox (2007) by Libby McDonald (page 91).
“Believe it or not, many brands of sippy cups contain bisphenol A. Some of the brands that do not contain polycarbonates are Avent Magic Cup; First Years Take & Toss; Gerber Color Change; and Playtex Sipster, Big Sipster, and Quick Straw.”