A component—；such as a respitratory mask—；for use in a user circuit for delivering a flow of a treatment gas to the airway of a patient includes a housing. The housing includes an exterior portion having a number of exterior surfaces positioned to be exposed to a surrounding environment. The housing further includes an interior portion having a number of interior surfaces (30) defining a passageway through the housing. The exterior portion has a first heat capacity and the interior portion has a second heat capacity which is less than the first heat capacity.
