I would allow scorpion (bladed) whips to have the metal portion made from special materials. But, a standard whip which is all leather would be tough. maybe you could home brew some variations of leather based off of different hides.
As "haft" is really just a synonym for "handle" or "hilt" and it isn't given its own game definition, and plenty of whips have wooden handles you could make a wyroot whip (you can attack someone with armor repeatedly for infinite ki/arcane pool with one)