flexatube

plural flexatubes

1. A folded paper puzzle created by connecting the ends of a strip of four squares, each folded along 45-degree diagonals. The solver is challenged to turn the structure inside out using only foldings.

   In the course of studying flexagons, Stone invented some fascinating objects, one of which was the tetra flexatube.

   1991, Theoni Pappas, More Joy of Mathematics: Exploring Mathematics All Around You

   2 more examples

   At least two other completely different methods of turning the flexatube inside out are known, and both are as devious and difficult to discover as this one.

   1958, Scientific American - Volume 198, page 126

   To create a different color for the inside of the flexatube: If using cardboard, glue two different colors together, back to back, before cutting squares into quarters

   2000, Mental math challenges, →ISBN, page 22