A mixing vessel for consumable liquids, comprising: a flask comprising: an internal chamber for receiving consumable substances for mixing, at least one consumable substance comprising a liquid, wherein the internal chamber is configured to receive a consumable liquid with a temperature greater than an ambient air temperature within the internal chamber, an outer wall, the internal chamber being located within the outer wall, and a heat sleeve, or a cavity between the internal chamber and the outer wall to thermally insulate the internal chamber; and a removable lid, wherein the removable lid comprises a sealing member to seal the internal chamber, the sealing member having at least a first stable spatial configuration (130-A) and a second stable spatial configuration (130-B) to change a volume of the internal chamber, and wherein the sealing member of the removable lid is arranged to transition between the first and second stable spatial configurations on application of a pressure generated within the internal chamber during mixing to increase the volume of the internal chamber, wherein the first and second stable spatial configurations are stable in the sense that the sealing member is constructed so as to remain in the respective first and second stable spatial configurations until an external force is applied, wherein, the sealing member is arranged to maintain the second stable spatial configuration (130-B) until an external force is applied to the sealing member, the external force being applied to an external surface of the removable lid. a flask comprising: an internal chamber for receiving consumable substances for mixing, at least one consumable substance comprising a liquid, wherein the internal chamber is configured to receive a consumable liquid with a temperature greater than an ambient air temperature within the internal chamber, an outer wall, the internal chamber being located within the outer wall, and a heat sleeve, or a cavity between the internal chamber and the outer wall to thermally insulate the internal chamber; and an internal chamber for receiving consumable substances for mixing, at least one consumable substance comprising a liquid, wherein the internal chamber is configured to receive a consumable liquid with a temperature greater than an ambient air temperature within the internal chamber, an outer wall, the internal chamber being located within the outer wall, and a heat sleeve, or a cavity between the internal chamber and the outer wall to thermally insulate the internal chamber; and a removable lid, wherein the removable lid comprises a sealing member to seal the internal chamber, the sealing member having at least a first stable spatial configuration (130-A) and a second stable spatial configuration (130-B) to change a volume of the internal chamber, and wherein the sealing member of the removable lid is arranged to transition between the first and second stable spatial configurations on application of a pressure generated within the internal chamber during mixing to increase the volume of the internal chamber, wherein the first and second stable spatial configurations are stable in the sense that the sealing member is constructed so as to remain in the respective first and second stable spatial configurations until an external force is applied, wherein, the sealing member is arranged to maintain the second stable spatial configuration (130-B) until an external force is applied to the sealing member, the external force being applied to an external surface of the removable lid.