Abstract: A tool for curing and bonding a honeycomb stack with void filler. The tool has a first tool piece with a cavity for receiving layers of unfilled honeycomb material and a second tool piece with a cavity for receiving at least one layer of void-filled honeycomb. The tool also has a compression seal arrangement that creates gas-tight seals between the first tool piece, second tool piece, and a barrier layer positioned between them, with a further seal covering the cavity of the first tool piece to form a gas-tight sealed volume including the first cavity, a pressure plate to cover the cavity of the second tool piece to apply pressure to the void-filled honeycomb, with a further seal to cover the pressure plate to form a gas-tight sealed volume including the second cavity.