A composite structure, and method of manufacturing it, having a specified width, length, and height defining a top and bottom the composite structure. The composite structure includes a three dimensional structural core constructed of a polymer with a first series of a geometric pattern repeated along its length. The structural core also has a second series of the geometric pattern repeated along the width thereof. The geometric patter may be a sinusoidal curve or a substantially pyramidal shape. The composite structure also includes a first reinforcement layer made of a polymer positioned above the structural core and bonded thereto. It also includes a second reinforcement layer made of a polymer that is positioned below the structural core and bonded thereto. The composite structure may also include a decorative layer above the first reinforcement layer, an acoustical batting layer positioned between the first reinforcement layer and the structural core, and may include fire retardant chemicals.