The present invention relates to an expression kit (2) for a breast pump (1) for extracting breast milk (101) from a human teat (102). The expression kit (2) comprises: a breast pump body (10) comprising a first pressure chamber (11) and a second pressure chamber (21) wherein the first pressure chamber (11) is configured for connection to a pressure unit (30) for generating a in the pressure chamber (11) wherein the second pressure chamber (21) comprises a breast-receiving funnel (22), a milk outlet (23) and a milk path (24) from the breast-receiving funnel (22) to the milk outlet (23) and wherein the first and the second pressure (11, 21) chamber are separated by a breathable membrane (50), which is gas-permeable and liquid-impermeable, for separating the first pressure chamber (11) from liquid in the milk path (24), wherein the breathable membrane (50) is a hydrophobic membrane. Further, the present invention relates to a breast pump (1).
