The Klein Bottle is a math joke, a surface with one side. Just as it's about to enclose space like a regular bottle, it curves back with a twist and the inner face merges with the outer – and suddenly inside and outside are one, like the side of a Möbius strip.

This neat trick can't quite exist in three dimensions, since the surface has to cross through itself, but at least we can make approximate models. This one is 3D printed in stainless steel, with some bronze for color. It's durable, washable and ergonomic, sized to fit the hand sweetly.

It's the perfect finishing touch for any math fan's kitchen, and you don't have to know a lot of geometry to enjoy it.

Yes, it really opens bottles!