Made from borosilicate glass for higher heat resistant. borosilicate is made out of boron trioxide which has a very low coefficient for thermal expansion. This allows it to resist heat by because it expands slower when exposed to extreme temperatures.
The bottom of the travel infuser unscrews for infusing. Simply unscrew it and add your loose leaf mix then screw it back on. It is recommended you add your mix prior to adding water. If you add the water first, simply turn the bottle onto its lid with the bottom facing up. Unscrew and add your mix, screw it back on and flip back to bottom down. Both the bottom and top of this glass can unscrew.