The third case described by Asakura and Oosawa is two plates in a solution of polymers. Due to the size of the polymers, the concentration of polymers in the neighborhood of the plates is reduced, which result the conformational entropy of the polymers being decreased. The case can be approximated by modeling it as diffusion in a vessel with walls which absorb diffusing particles. The force, , can then be calculated according to:
In this equation  is the attraction from the osmotic effect.  is the repulsion due to chain molecules confined between plates.  is on order of , the mean end-to-end distance of chain molecules in free space.