Optimization of the backwash operating conditions for a specific membrane-feed system can become an initial step to reduce energy and ultrafiltrated water consumption. In this work, fouling removal mechanisms of bentonite cakes were investigated on ultrafiltration Kynar® polyvinylidene fluoride (PVDF) hollow fibre membranes having different dimensions, mechanical and surface properties and water permeability. The study on different bentonite cake structures, formed in dead-end filtration at constant pressure and in outside-in mode, has demonstrated that cake removal mechanism was mainly governed by the backwash flux and not by the intrinsic membrane properties. We define a critical backwash flux, from which backwash becomes efficient. The critical backwash is related to a critical inter cake-membrane pressure which occurs at the cakemembrane interface during backwash, which really acts on the deposit. A fouling removal mechanism is thus proposed involving three steps related the critical inter cakemembrane pressure. The critical inter cake-membrane pressure required for an efficient backwash was independent of the membrane properties and bentonite hydraulic resistance. The critical backwash flux can be used to optimize the energy efficiency of the ultrafiltration process.