The antique ones I've seen have one of 2 methods. One is called birthing or pillowcase style. The other is a modified version of the same. You make a batting, strip of backing and top sandwich, sew along the edges of the hexies and cut away the excess, and turn it right side out then hand sew (!) a center backing panel over the rest of the back. What I have NOT seen is any binding. These edges, I'm told, are called "knife edge".