Bromane Hair Filling Density Fibers are made from cotton. I like using them because it's sustainably sourced and much better for the environment than animal keratin is. If you're vegetarian/vegan that's one benefit right off the bat.
Interestingly enough I also find that the Bromane cotton fibers are fiber than Toppik and so they lead to better coverage but still preserve texture well - so it doesn't look like you're "painting your scalp".