The Oxo Tot Glass Baby Blocks Freezer Storage Containers are made of durable borosilicate glass. They're naturally thermal shock resistant, which means they can go directly from the fridge or the freezer into the oven or microwave. They can also go in your diaper bag thanks to their uniquely designed, leakproof lids. Use the measurement markings on the side to portion out homemade baby food or snacks, nest the Blocks in the included stackable tray, chill and just grab what you need as you need it. When it's time to clean up, you can remove the seal from the lid for extra thorough cleaning.