When I first heard of 100% castor bean oil toothbrush bristles my bullsh*t meter immediately went off.
How would a bristle, that is very much a solid, be made of 100% oil, which is very much a liquid?
It made no sense to me. Digging deep into the research and studies, I learned like all things in the sustainability realm, the truth is weird and unobvious.
SO, WHAT'S IT MADE OF?
Simplistically, castor bean bristles are made by extracting castor oil from the castor seeds by a mechanical pressing process. The oil is then processed, processed again, processed into a granular form and then processed again into bristle-form.
If it sounds really "processed" that's because it is.