What do you think the most important quality should be in our new tea tumblers?

I want to have a way where I can steep the leaves on-the-go, without making a mess.

I want to make sure that the glass is properly insulated. So that I won't burn my hands when I add hot water.

I'm a Road Warrior! I want to trust that my tumbler is leak-proof and won't spill liquid when I'm traveling.