A firm worsted twill fabric with a steep angle and a pronounced line, very similar to gabardine, named after the punctilious fictional Belgian detective, Hercule Poirot. This textile was designed for the rigorous standards of the tailoring world, which demands good looks and durability in equal measure. Poirot twill is such. I have only ever come across it in coats and jackets found in vintage clothes shops, and do not know whether it is still in production.