Patent ID: 7208223

Claim:
A composite sheet material comprising: a rigid core ( 34 ) of honeycomb cellular material having a first and a second side and an initial thickness; and the rigid core ( 34 ) being formed of a plurality of individually extruded tubes arranged adjacently and in parallel and in a hexagonal pattern to form a honeycomb structure in which each tube has a first end in contact with a first side skin and a second end in contact with a second side skin; the first skins is formed of continuous sheet material on the first side of the rigid core and the second skin is formed of continuous sheet material on the second side of the rigid core and the first and the second skins each have an initial thickness; and the first and the second skins ( 32 , 36 ) are formed of a reinforced thermoplastic laminate thermoformable in a temperature range of 150° C. to 300° C.; and the tubes are formed of polyetherimid material thermoformable in a temperature range up to 170° C.; and the composite sheet material being formed of the rigid core ( 34 ) and the first and the second skins ( 32 , 36 ) is uniformly compressed while heated to a temperature in a thermoformable range of 150° C. to 170° C. so as to have a uniform thickness less than a sum of the initial thickness of the rigid core ( 34 ), the first side skin ( 32 ) and the second side skin ( 36 ); wherein in each tube, regions of a wall of the tube adjacent the first and second ends of the tube are distorted so as to bridge interstices between the first ends and the second ends of each adjacent ones of the tubes to thereby increase the contact surface area between the tube and the first side and the second side skins and walls.