“T-Ester” is a new material that combines the high transparency of glass with the lightness of plastic. It has high heat resistance (110°C) and is compatible with boiling sterilization, steam sterilization, and chemical sterilization. Both bottles were sterilized after purchase, but were not used as I was using a different baby bottle. Please understand that these items have been opened and stored by a private individual before purchasing. Please be sure to wash and disinfect the bottles before use after they arrive. Thank you for looking.