With Dr. Brown's Natural Flow Options plus Glass narrow baby bottle, your options have never been better. The Options plus bottle is designed from the ground up to make feeding your baby comfortable. Each is specifically designed to give the same steady, natural Flow, starting at the top, so you and your baby know what to anticipate at every feeding. The anti-colic vent mechanism makes it easy for baby to feed while the soft silicone aids in natural Latching. Additionally, our glass bottles are composed of pharmaceutical-grade borosilicate glass, which is heat and thermal shock-resistant and can endure hot and cold temperatures as well as progressive temperature fluctuations, making Dr. Brown's the top physician recommended bottle in the world.