A humidifying apparatus utilizing a semi-permeable membrane portion within a gas conduit where the direction of gas flow within a central lumen is given by an arrow. The humidification apparatus has a helical configuration for the semi-permeable membrane portion, a structural reinforcing member or members, a water channel and a heating element. The helical configuration of an outer wall may be similar to conventional conduits that are in common use in respiratory apparatus. Thus the humidification apparatus may be readily substituted into existing respiratory device by exchanging the gas conduit.