I have tried a few different styles of folding based on instructions from floral friends in Asia. They obviously have access to a better quality banana leaf than me, however I have had success with flax and agapanthus leaf.
This technique is included in a video tutorial along with palm frond weaving, autumn/fall leaf containers, reed weaving (corn dolly style), foliage domes, offcut shapes and spider webbing.
Here is the section on leaf folding:
