Firstly, sort the hair by length. During this process, you should remove any hairs that are damaged or otherwise not up to standard.
Then, separately place hair into bundles by length.
Tie them into a larger bundle that includes the entire ponytail with all the lengths.
Finally, you get a bunch of smaller bundles inside of a larger bundle of hair.
For virgin hair that is not color processed, the “processing” stops right there and the hair is then sewn into a wig or hair-piece.