A
fiber-reinforced
composite structure has two molded outer polymeric
layers spaced apart from each other and defining a cavity therebetween. Each molded outer polymeric layer defines a sealing surface extending about a periphery of the respective layer, and the opposing sealing surfaces cooperate to define a
hermetic seal extending about a periphery of the cavity. One or more multi-directional
fiber reinforcement
layers are adhesively attached in a discontinuous manner to each outer polymeric layer, and define a first region of the cavity extending between each respective outer polymeric layer and adjacent
fiber reinforcement layer, and a second region of the cavity extending between the
fiber reinforcement layers. A core is located between the two outer polymeric layers, and is made of a resinous core material capable of exhibiting a foamed character and a resinous character. The resinous core material has a
blowing agent activatable upon
exposure to a predetermined
vacuum pressure within the cavity to convert the core material within the second region of the cavity from a resinous character to a foamed character and thereby fill the second region of the cavity with the foamed core material. Each multi-directional
fiber reinforcement layer is impregnated with the core material exhibiting a relatively dense, resinous character, and each first region of the cavity is substantially filled with the core material exhibiting a resinous character to fixedly secure the multi-directional
fiber reinforcement layers to the outer polymeric layers. A structural insert, such as a rigid plate adapted to receive fasteners, is embedded within the core material for attaching other devices or structures thereto.