All else being equal, heavier molecules diffuse:

1. Diffusion rate depends on several factors, one of which is the mass of the moving particle. 2. A heavier particle is harder to accelerate at a given temperature. 3. Heavier molecules move more slowly, therefore they diffuse more slowly. 4. The reverse is true for lighter molecules. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 5 'Structure and Function of Plasma Membranes', sections 5.1-5.4_