Möbius strip or sheet - a surface which is formed by bonding a rectangular sheet so that opposing vertices are connected.

This is a non-orientable surface, which is one-way, ie, when moving across the surface without crossing the boundaries, it can be a starting point, but on the other side of the sheet.

instructions

1

Take an elongated strip of paper rectangular ABB1A1.

2

Fold the sheet so as to coincide with the vertex A vertex B1, B and the vertex coincides with the vertex A1. Glue the ends of the sheet, the resulting surface will be a sheet of Mobius.

3

The resulting tape does not fall apart if it is cut at the middle line, it will turn into a one-sided, double-twisted surface.
If we continue to cut two or more twisted sheets, then there are more amazing pieces such as "trefoil knot" or "Paradromnye ring."

4

If you glue the two Möbius strip together along the edges, you get a figure, called "Klein bottle". In a typical three-dimensional space to build it is impossible without self-intersections.