Our baby bottles are made of the highest quality, thermal shock resistant borosilicate glass. This allows our bottles to transition safely from freezer to boiling water. The silicone sleeves provide a good gripping surface for little hands and help protect against the occasional drop. - Protective medical-grade silicone sleeve provides a tactile non-slip gripping surface and helps prevent breakage - While very durable, our bottles are still glass and are not unbreakable - Dishwasher safe (place cap parts and nipple on top rack/no need to remove silicone sleeve unless desired) - As baby grows we offer a range of caps (sippy and flat) to extend the life of your bottle - Includes polypropylene (PP#5) cap, ring and stopper.