thermoplastic structural components utilized within building construction as permanent formwork . the components formed with openings along a length which serve to allow concrete to flow from one form to adjacent forms . thus , filling the components forming a surrounding wall of a building . the openings allow for air circulation within components forming a roof assembly . the components are co - extruded with a protective skin along outer surfaces thereof . grooves are provided along the length of the component for mating with interlocking flanges of a box connector . planar spaced walls are provided within each component and have a series of openings along a length thereof .