Yesterday I began covering enough equilateral triangles to make 4 tetrahedrons, and I just finished #16 this afternoon. As I tidied the work area gathering up the threads and snippets, I heaped the triangles into a neat pile, and it struck me how much these cream triangles looked like sandwiches or cut bread! So I set them on a plate for a pic or two –
Starting from the lower RH corner, the next pic shows template plastic with cream fabric machine sewn to one side and trimmed; heat activated batting triangles glued to triangular shapes of cream fabric; and finally the edges hand sewn in place all round a triangle shape.
So if you want to try them yourself, you have all the knowledge you need, except to practice slip stitching the edges together in such a way that very little stitching shows – use matching thread+skill. OR one could make the stitching up each join part of the surface decoration.