The resistance in series and force balance model has been extended to include the wide size distribution and compressibility of the feed particles. The model successfully explained the experimental results obtained during crossflow microfiltration (CFMF) of lactalbumin particles under varying operating, feed and membrane conditions. The possibility of applying the developed force balance model to obtain a desired size separation without changing the membrane pore size was successfully demonstrated. There is scope to apply the models to other widely size distributed compressible particles, e.g. particles of biological origin.