Heat-sterilizable membranes are disclosed comprising at least two hydrophobic polymers which are normally immiscible with each other, and in which at least one of the hydrophobic polymers is normally unstable under sterilization conditions while at least one of the other hydrophobic polymers is normally stable at sterilization conditions, and in which the at least two hydrophobic polymers are compatibilized with each other so that the membrane formed therefrom is stable at such sterilization conditions.