Functionally graded (FG) materials provide the solution to spatial and temporal control of material properties with smooth transition at different length scales of the material structure. Tailoring material properties is becoming a necessity to the evolving products that have certain design requirements. Smooth transition at different length scales is important to eliminate abrupt change of material properties and microstructure which avoids stress jumps and other structural problems like delamination. Two challenges are associated with FG materials, i) fabrication procedures with correlation to the microstructure and mechanical properties, and ii) the numerical treatment of FG materials that accounts for the microstructural details and gradient. This research addresses both challenges with enough depth to design FG porous polymeric materials. The fabrication process focused on developing FG porous structures and stitched composites. Different processing parameters were successfully correlated to the microstructure and showed the potential to produce structures with desired features. The microstructure was further correlated to mechanical properties like creep compliance and impact energy absorption. This motivated the development of numerical homogenization procedures that help in conducting numerical experiments with FG structures. A statistical based homogenization model was developed, which accounted for the microstructure gradient. The model was implemented to higher order plate theory with stretching terms, and provided accurate results compared to experimental data. To alleviate the dependency on experimental data which was the drawback of the statistical model, a purely numerical procedure was developed which is based on 3D reconstruction of the microstructure to statistically reduce the system but preserve the same main features of the parent structure. The model was in good agreement with experimental results. This makes the homogenization procedure independent in providing details about mechanical properties for an assumed graded porous structure or composite. Combined with the processing-microstructure graphs, the numerical tool can be used in an inverse-homogenization procedure to make graded porous structures with desired mechanical properties.