Is the Series 2 Flip lid leak-proof?

No - Whilst the Series 2 Flip Lid has been designed to be spill-proof but it is not completely leak-proof so we recommend transporting it in an upright position or in the side pocket of a rucksack.

However, you do have the option make your Flip Bottle leak-proof by making the switch from the Flip Lid to the Series 2 Bottle Lid and Collar which can both be purchased here.