A mixing device, for a mixable material, has at least one cartridge and a closure piece. The cartridge contains a first component of the mixable material and has a cartridge head in which at least one air opening is arranged, and the closure piece is arranged on the cartridge head in such a way that the at least one air opening in the cartridge head can be closed and opened by the closure piece. The closure piece is mounted so as to be rotatable or slideable relative to the cartridge head, and a connection extends through the cartridge head or a cartridge wall into the interior of the cartridge and connects the interior of the cartridge to a container for a second component of the mixable material.
