Just a quick note to parents and other users of the brilliant AnyWayUp cups (“the world’s only totally non-spill cup”): don’t use them with fizzy drinks.

The cups rely on a slight pressure imbalance to keep the liquid from leaking out. You take a few sucks, the pressure inside the cup drops, and this is enough to keep the rubber valve nicely closed. But as soon as you put a carbonated beverage in the cup, the CO2 escaping from the drink creates an overpressure in the cup. If you hold it upside-down, this overpressure is enough to force liquid out through the valve, and also out through the rim of the cup. Messy.

Apple juice, yes. Appletise, no.