Most crochet braids (crochet weave) use synthetic bulk braiding hair in a curly style for their crochet braids for 3 main reasons:
- Many people cut the braiding hair used for crochet braids as they take it out, or at least do not try to reuse it, so human hair would not be practical because of the cost.
- The synthetic bulk braiding hair used for crochet braids tends to start to frizz at the ends after a time and so trimming of the ends is necessary, thereby eventually reducing the length of hair that is left. Not all frizz can be cut out though, so eventually the synthetic hair will need to be replaced so as to not look ratty.
- Human hair has a cuticle. The way that crochet braids are applied with doubling and knotting would not allow the cuticle to face in the right direction, although I do think some types of human hair might work. (I will admit, I am not an expert on human hair used for weaving.)
The synthetic fiber that seems to be most favored is Kanekalon or a Kanekalon and Toyokalon mix, which can now be manufactured to closely resemble human hair in texture, but with less tangling that human hair, although the quality among brands seems to differ.
Choosing a curly style of synthetic hair for crochet braids helps to cover the cornrows, although some people do use straight hair.
Flame-resistant straight Kanekalon could be used and then curled afterward, either with a curling iron (after wetting the hair) or using some type of rollers and dipping the hair fiber in near-boiling water.
Other popular choices are Freetress or Model Model bulk synthetic braiding hair in one of their curly styles.