A blister assembly comprises at least one collapsible blister adapted, as it is collapsed, to eject a liquid contained therein. The blister assembly comprises a first layer (130) having at least one blister chamber (150) and a second layer (131) sealed to the first layer at least around a periphery of the at least one blister chamber such that a liquid is contained between the first layer and the second layer. The seal between the first and second layers comprises a first planar portion having a first peel strength and a second planar portion having a second peel strength, wherein the first peel strength is greater than the second peel strength, such that when pressure is applied to the blister, the second portion of the seal breaks to release the liquid contained within the chamber into the liquid inlet. The blister assembly further comprises at least one discontinuity (142) formed in the first and second layers in the region of the first portion of the seal, such that a shear force is required to delaminate the first and second layers in that region.