An analytic model for the width of the electron density transport barrier shows qualitative and quantitative agreement with systematic data obtained in the DIII-D tokamak. The width of the barrier in H-mode decreases as the pedestal density increases. Moreover, for L-mode and H-mode density profiles with the same pedestal density, the gradients of the barriers are of similar magnitude even though the temperature and pressure gradients are much larger in H-mode. These results are consistent with the hypothesis that neutral penetration provides important physics which helps to set the width of the H-mode barrier for the electron density.