The present disclosure relates to a packaging system for producing a foam-in bag and method of mixing foam for the packaging of articles for shipment and storage, and in particular, to an improved, flexible, multilayered packaging system with a vented, deformable outer bag and an inner confinement structure made of paperboard box or a plastic bag with reclosable opening for optimal mixing and controlled release of the foam using preferential paths, score lines, weakness points, and/or obstacles to flow. In addition, the precursor fluids are placed in individually sealed pouches with calibrated and aptly positioned frangible seals to facilitate mixing after rupture inside of the inner confinement structure. In another embodiment, one of the precursor fluids is placed directly in the inner confinement structure, and in yet another embodiment, both sealed pouches are adhesively joined to the inner confinement structure. What is also disclosed is a method of mixing foam precursors in the different embodiments of the foam-in-bag packaging system.