An example of a non-FRP layer in a pipe is referred as a reinforced silica-filled core to provide optimal bending stiffness. The other non-FRP core materials are usually used for sandwich panels that can be rigid polymeric foams, wood or honeycombs. These cores have sufficient shear strength to withstand transverse shear stresses and they provide high shear stiffness to resist buckling. However, the tensile and compressive stresses on the core is less than the face sheets. The thickness of this layer is variable depending on application. The focus here is on non-FRP fillers added to increase bending stiffness of the structure.