The Klein bottle is a fascinating topological shape first described in 1882 by German mathematician Felix Klein. It's what's called in mathematics a non-orientable, one-sided surface with no boundary. An orientable surface is one that can't be transformed into its mirror image by moving a shape along the surface. This means that the both the Möbius strip and the Klein bottle are non-orientable. To further enjoy this unique and visually delightful shape, we've made adorable tiny glass Klein bottles necklaces! The Klein bottles are handmade from high borosilicate glass and come on your choice of a 24 inch steel chain, adjustable brown leather cord, or adjustable black leather cord. The bottles measure about 1.5in (~37mm) from top to bottom. They function properly, with a tiny opening all the way through the neck and into the bottle.