The present invention provides a thermally insulated shipping container 1 comprising a thermally insulating layer 5 defining a first void, a main layer 9, 10, 11 containing phase change material (main PCM layer) within the first void and defining a second void within the first void, a barrier layer 12 containing phase change material (barrier PCM layer) within the second void and distinct from the main PCM layer, the barrier PCM layer 12 defining a third void within the second void, the container being arranged to receive a product for transportation inside of the third void, wherein the main PCM layer 9, 10, 11 has an average thickness greater than the average thickness of the barrier PCM layer 12, the barrier PCM layer 12 comprises of an envelope in which the phase change material of the barrier PCM layer 12 is contained and the barrier PCM layer 12 is configured to maintain the phase change material with a relatively even distribution within the envelope.