Borosilicate Baby Jars & Sippers made available by us are very efficient and safe for use. This glass is resistant to heat as it is formed by silica and boron trioxide, two chemicals that are safe. Other than these two chemicals, soda ash and alumina are used in the making of this kind of glass. Borosilicate glass is more durable and has better optical clarity than traditional soda lime glass. The glass also has higher thermal shock resistance, meaning, when encountering rapid change in temperature, the glass has better resistance to cracking and breaking. The Borosilicate Baby Jars & Sippers are very easy to use.