An insert (l4) for a breast pump of the type comprising a milk reservoir, an essentially rigid suction bell (ll, 2l) having a flared open end, and a suction means for temporarily reducing an ambient pressure within said pump; the insert (l4) is formed of a soft and resilient polymer material that is inert against water at a temperature of at least about l00 DEG C and is a substantially monolithic self-supporting structure consisting essentially of a funnel-shaped first portion (l43) for a sealing contact with a nipple-encompassing area of a mother's breast when said ambient pressure is reduced within said pump, and an elongated thimble-shaped second portion (l47) capable of defining an enclosure (l49) around said nipple-encompassing area when said ambient pressure is reduced within said pump; the funnel-shaped first portion (l43) of the insert structure (l4) provides an annular deformation zone (l45) having a predetermined wall thickness; the elongated thimble-shaped second portion of the insert structure (l4) comprises a longitudinal wall section (l42) and a transverse end wall section (l44) having at least one perforation (l9) for permitting milk to pass to said reservoir; the second portion (l47) is formed and dimensioned so as to prevent axial collapse thereof under normal conditions of use and has a wall thickness that is greater than the predetermined wall thickness of the deformation zone (l45).
