There's an overlap of paper on both sides of the intrinsic straight crease, which is curved in the final model. Robert Lang calls the couplets flanges in his flanged pots. We can, of course, have two intrinsic straight creases for the couplet. The surface of the model will then be polyhedral.
Cheng Chit
What is the best paper to use? Warps can be a problem.
