A material dispensing unit (1; 10) for a three dimensional printing apparatus (100; 200) has a nozzle (3) for depositing particulate material (5; 220a, 220b; 224; 226) on a build surface (7), where the nozzle defines a through passage (9) for the material. The through passage has an inlet end (11) for receiving the material and an outlet end (15) for dispensing the material. A valve (21) is provided at least one of at, within or in fluid communication with the through passage for controlling flow of the material via the through passage, the valve being operable between open and closed positions. Flow of said material into the through passage is blocked when in the closed position and, when in the open position, flow of the material into the through passage is allowed. A method of forming a three dimensional object (31) is also disclosed, as is a three dimensional printing apparatus (200) comprising one or more dispensing units (la; b) for dispensing particulate material (220a, 220b; 224; 226), an enclosure (137) for containing the material dispensed by the one or more dispensing units and one or more heating elements (210, 212) for heating the material contained in the enclosure to a first predetermined temperature.
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