A method of forming a composite structure including coupling a plurality of components together forming a joint: wherein the plurality of components are oriented to form a radius gap therebetween: forming a filler structure that includes a closed cell foam core that has a porosity within a range defined between about 20 percent and about 40 percent by volume of the closed cell foam core and wherein the closed cell foam core is formed from a silicone-based material. The method also includes positioning the filler structure in the radius gap: and applying at least one of heat or pressure to the plurality of components and the filler structure.

A composite structure is provided. The composite structure includes a plurality of components coupled together forming a joint, wherein the plurality of components are oriented such that a gap is defined at least partially therebetween. A filler structure is positioned in the gap, and the filler structure includes a closed cell foam core.