Bunka is a sort of chain-stitched/braided 4-ply rayon 1/16" round cord. It is unraveled or 'pulled' to make a tiny curly strand. You just find the right end and pull a thread. Bunka has many uses; some make curls for doll hair and some use it for trim on costumes and hats.
Here is a link to some some information about Bunka:
And here is, a video demonstrating the unraveling of Bunka to get those curly threads: