Trihexaflexagon is constructed by cutting a strip of paper so that it may be marked off in 10 equilateral triangles (A). The strip is folded backward along the line ab and turned over (B).

Start with a square paper in the chosen colour. Fold it diagonally, joining opposite corners to create a triangle. Unfold and ...

If using standard rectangular printer paper, fold one corner diagonally until the edges align, then trim off the excess to ...