Cut a strip of paper with an even width. The width and length should be at least 1:4 or 1:6. I just cut a rough length that looks long enough and adjust the final length as I make it. Fold a small triangle on one end.
Fold backward at the end of the triangle and repeat fold like an accordion.
Fold the straight lines between the diagonals again to change the fold direction
Form the ‘Triangular Bipyramid’ by rolling the shape along.
Wrap around the faces a couple of times to form a solid shape, trim off the end triangle and insert the final triangle part into a slit to close it up.