An insert for a breast-receiving funnel (10) of a breast pump comprising an elongate inflatable bladder (23) which defines a pressure chamber (26), the elongate inflatable bladder (23) being adapted to fit in a teat receiving space (11) of said breast receiving funnel (10) so that the bladder extends from an inner end of said funnel towards an outer end of said funnel, and lie 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 said user's teat, to aid the expression of milk therefrom.