When searching for a more stylish water bottle, check out the Kai 540 ml bottle. This single-wall bottle is made of borosilicate glass. It is a type of glass that is stronger and lighter than regular glass and BPA free. The bottle is wrapped with a soft silicone sleeve to ensure a secure grip. Furthermore, the Kai is finished with a bamboo screw-on lid and a non-slip bottom, so the bottle can't just fall over. The bottle is delivered in a neat Avenue gift box. Not suitable for the microwave.