(EN) A cap assembly for a refill capsule and associated refill system is disclosed. The cap assembly (200) comprises an inner wall (202) defining a conduit (203) through the cap assembly (200) and an outer wall (204) surrounding the inner wall to form a circumferential void between the inner and outer walls (202, 204). A connecting wall joins the inner and outer walls (202, 204). The cap assembly (200) further comprises a closure member (208) which is sealed to the inner wall (202) with a peripheral frangible connection (210). The frangible connection (210) is disposed between a first peripheral recess (222) formed between the inner wall (202) and the downstream side (208b) of the closure member (208), and a second peripheral recess (224) between the inner wall (202) and the upstream side (208b) of the closure member (208).