A fuel tank cap includes a housing having a side wall, a bottom wall, and a receptacle, a fuel vapor adsorption material positioned within the receptacle, an inlet at least partially defined by the bottom wall and configured to provide fluid communication with a fuel tank vapor space, an outlet at least partially defined by the bottom wall and configured to provide fluid communication with the atmosphere, an internal wall extending from the bottom wall at least partially into the receptacle, and an aperture at least partially defined by the internal wall and configured to permit fuel vapor to flow in a vapor flow path from one side of the internal wall to the other side of the internal wall.