Abstract: A thermoformed dual-compartment flexible package and method for storing and dispensing the components of a polymerizable system such as the base and catalyst portions of an addition cured dental impression material. Mutually reactive constituents are isolated during storage. A first embodiment of the package includes two thermoplastic cups each having an open mouth circumscribed by an annular groove, separated by a slotted aperture. The package further includes a thermoformed flexible closure having a central projection between two annular projections. Two seals are formed by engaging the annular projections within the grooves. A second embodiment includes two thermoplastic cups separated by a slotted aperture, with each cup having an open mouth from whose rim depends an outwardly canted wall terminating at a recessed lip.