In the mid-1960s an alternative hypothesis (the "partition–diffusion model") sought to establish that the water molecules partitioned between the water phase and the lipid phase and then diffused through the membrane, crossing it until the next interphase where they left the lipid and returned to an aqueous phase.
Pada pertengahan 1960-an, hipotesis alternatif ("model partisi–difusi") berusaha menetapkan bahwa molekul air terpartisi antara fase air dan fase lipid serta kemudian berdifusi melalui membran, melintasinya hingga interfase selanjutnya, meninggalkan lipid dan kembali ke fase air.