The invention relates to a valveless spacer device for a metered dose inhaler (MDI), the spacer device comprising a body having an inlet and an outlet opposed from the inlet, a demountable, flexible bag attached to the body, the bag and body together defining a chamber, such that the inlet and outlet are in fluid flow communication with an interior of the chamber, wherein the inlet is configured to be connected to an MDI containing a drug to be inhaled and wherein the flexible bag, following actuation of the MDI, serves as a reservoir allowing for the formation of a cloud or mist of the drug therewithin which is then ready for inhalation, the flexible bag being configured to be at least partially deflatable and at least partially inflatable commensurate with a single breath and/or rebreathing.
