A 20 oz stainless steel tumbler built around a vacuum between two walls, which is the most effective way of keeping a drink at the temperature it started at. Hot coffee stays hot on a long commute and iced water stays cold through an afternoon outdoors.
The vacuum layer also means no condensation forms on the outside of a cold drink and no heat comes through from a hot one, so it sits on a desk without a ring underneath and can be picked up straight after pouring.
The handle is the detail that separates this from a plain tumbler: it hooks over a finger while you carry something else, and gives a firm grip on a full cup. Steel does not hold the taste of yesterday's coffee the way plastic does.
