Composite panel having in-situ thermoset foamed core

A method for making a composite panel having a honeycomb core sandwiched between a pair of facing sheets, the honeycomb core comprising a pair of opposed sides and a plurality of contiguous cells with interior walls, the method comprising the steps of:

• (a) coating the interior walls of the cells with an unexpanded thermo-expandable material by coating interior walls of elongate cells within a honeycomb block with a unexpanded thermo-expandable material and then slicing the honeycomb block along a plane substantially perpendicular to longitudinal axes of the cells within the block to create a honeycomb core having coated interior walls;
• (b) bonding a pair of facing sheets to the opposite sides of the honeycomb core;
• and
• (c) heating the honeycomb core while the honeycomb core is sandwiched between the pair of facing sheets with sufficient heat to cause the thermo-expandable material to expand and to at least partially fill the cells.