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

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).

WHAT YOU NEED: two pieces of paper/card, pencil ... STEP 3: Take one of the triangles and use the ruler to fold a vertical line down the middle. Cut along the fold. You should now be left with ...