Nacelles are provided having a tubular casing, open at its opposite axial ends, with an inner wall and an outer wall which are connected to each other at the front end along a leading edge and at the rear end along a trailing edge and which enclose, together with the leading edge and the trailing edge, a cavity. To prevent the formation of ice at least in the zone of the leading edge of the nacelle, a separating member made of porous material is arranged inside the cavity to divide the cavity into an inner cavity, between the inner wall and the porous separating member, and an outer cavity, between the outer wall and the porous separating member, and to put the inner cavity in fluid communication with the outer cavity only in a front zone of the cavity in contact with the leading edge, and a two-phase fluid is contained in the cavity.