A nasal delivery device for delivering substance to a nasal cavity of a subject, the delivery device comprising: a substance supply unit for supplying a dose of substance to be delivered to the nasal cavity of the subject, the substance supply unit including an inlet and an outlet; a nosepiece unit including a nosepiece for fitting to a nasal cavity of the subject and being in fluid communication with the outlet of the substance supply unit; and a mouthpiece unit including a mouthpiece in fluid communication with the inlet of the substance supply unit and through which the subject in use exhales such as to entrain substance from the container chamber and deliver the same through the nosepiece, and at least one temperature modifier for reducing a temperature of the exhaled air flow such as to reduce the absolute humidity thereof.