Back of a cloth headband?
If you're asking about something other than the usual ribbons to tie under the chin like a headdress, so you can hook and clasp it under the hair, I've always cheated and attached an extra stretchy length of elastic to both ends of the cloth and then used it as a regular stretchy headband.
It's what I did with this headdress:
01 02 03And even Moi meme Moitie has been known to use that trick.