# Math Insight

### A Möbius strip is not orientable

A surface is orientable if it has two sides. Then, one can orient the surface by choosing one side to be the positive side.

Some unusual surfaces however are not orientable because they have only one side. One classical examples is called the Möbius strip. You can construct a Möbius strip by taking a strip of paper, twisting it half a turn, and then taping the ends together. A Möbius strip with a normal vector is shown below.