Klein bottle has no edges and do not apply to it the concept of "inside" and "outside"

Klein bottle - a definite non-orientable surface (ie, two-dimensional manifold). Klein bottle was first described in 1882 by the German mathematician F. Klein. It is closely related to the Möbius strip: If the Klein bottle cut in half along its axis of symmetry, the result is a Mobius strip. The name apparently comes from an incorrect translation of the German word Fläche (surface), which in German is close in spelling to the word Flasche (bottle); then the name returned as such in German.

To build a model of a Klein bottle, you need to take a bottle with two openings: in the bottom of and in the wall, pull the neck, bend it down and sell it through a hole in the wall of the bottle (for true Klein bottle in four-dimensional space of the hole is not necessary, but without it you can not do in three-dimensional Euclidean space), attach to the hole on the bottom of the bottle.

Unlike ordinary glass of this object has no "edge" where the surface of the sharp end. Unlike the balloon can go all the way from the inside out without crossing the surface, that is, in fact, this object has no "inside" and no "outside».

via factroom.ru