Molten resin infused with supercritical fluid via the MuCell process is injected into a thin mold. It expands quickly to fill the mold. The back of the mold is then partially extracted (core back) to form a thick, low-density, multilayer structure. The cross section shown is 6 mm deep. Door-panel liners are particularly well suited to the weightsaving combination of core back and MuCell.