Caliber Gourmet Bullet Thermos Bottle 17oz (500 ml) the bullet shaped thermo is the prefect size for keeping hydrated outdoors and fits perfectly in your bag or lunch box. The Leak Proof lid design allows for the bottle, thermos or flask to be able to turn in any direction, and unlike a regular portable cup, mug, carafe or water bottle ours when securely closed is spill and leak proof. Caliber Gourmet Bullet Thermos tumbler is designed to help your coffee, tea, soda, hot chocolate, fruit water, or other favorite caffeinated or non caffeinated drink last up to 12 hours. This will definitely cover most work days. they chose 17 oz because its bigger than 16 oz portable cups, mugs, flasks with lids and other smaller funtainer sized bottles while being more portable, light weight and easier to carry on the go than 20 oz containers.