The noodles included are usually rice vermicelli, and the ones I had in my bowl were kind of rounder and slightly chewier than the noodles I had, for instance in bowls of pho, which were more silky and soft.
Also, unlike pho that has a thin clear broth usually prepared by boiling bones and meat with herbs, the soup stock used for bun mam has a far different look and taste.
The broth is flavored, most importantly with fermented fish sauce.