The invention discloses a valve including a valve body with a valve inlet and a valve outlet. The valve body is joined to a bellows between the valve inlet and the valve outlet, the bellows having an annular side wall formed in a concertina formation with inner and outer corners wherein the side wall has a non-constant thickness along its length, the side wall being thicker at the outer corners and thinner at the inner corners. The bellows further has an annular mounting base for attachment to the valve body. The valve body has an annular flange from which extends an upstanding collar, wherein the mounting base is clamped between the valve body and the collar. The mounting base has a width being wider than a gap formed between the valve body and the collar so that the mounting base is compressed when clamped between the valve body and the collar.