Aside from being perfectly symmetrical, loaves baked in these kinds of pans have a very thin crust and a soft, finely-textured crumb. In fact, these loaves are called pain de mie in French, which literally means "bread of the crumb." These loaves are perfect for sandwiches.
Many pumpernickel bread recipes also call for using a Pullman pan. It helps to get that dense, chewy crumb and to keep the loaf from drying out during the traditionally long baking time.
Pullman pans can be found at most any well-stocked kitchen supply store. You can also order them online:
What have you baked in your Pullman pan?
(Images: King Arthur Flour Blog)