A composite, lightweight, fire-retardant laminar structural panel (10, 10', 10", 30) of the present invention comprising: (i) a sheet-like central honeycomb core (11) formed of aluminum, paper treated to improve its fire resistance characteristics, or the like; (ii) upper and lower imperforate face sheets (15, 16) formed of lightweight fibrous materials impregnated with a phenolic resin; (iii) a pair of upper and lower phenolic adhesive films (18, 19) interposed between the honeycomb core (11) and respective ones of the imperforate face sheets (15, 16) for adhesively bonding the face sheets (15, 16) to opposite sides of the core (11); and (iv), a fire-retardant coating (20) comprising a copolymer of vinylidene fluoride and hexafluoropropene applied to at least the exposed surface of the lower face sheet (16). In certain of the exemplary forms of the invention herein described, the composite, laminar panels (10, 10', 30) are designed to provide one of a plurality of different load bearing capacities dependent upon the type of use to which the panel is to be put; while in other exemplary forms of the invention, a given panel includes regions of differing density and/or of different numbers of face sheet plies; but, which is of uniform overall thickness so as to provide relatively high load bearing capacities in high traffic and/or high load environments and relatively low load bearing capacities in low traffic and/or low load environments.