An insert for a breast-receiving funnel of a breast pump includes an elongate inflatable bladder which defines a pressure chamber. The elongate inflatable bladder is configured to fit in a teat receiving space of the breast receiving funnel so that the bladder extends from an inner end of the funnel towards an outer end of the funnel. The bladder lies between a user's teat and the funnel when a breast is inserted in the funnel, such that the elongate inflatable bladder is configured to deform towards a user's teat located in the teat receiving space in a predetermined manner when a pressure difference is applied between the teat receiving space and the pressure chamber such that a peristaltic action is applied to the user's teat, to aid the expression of milk therefrom.