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Manufacturing turns a design and raw materials into physical products through controlled processes such as casting, forming, machining and joining. The process changes more than shape: heat treatment and deformation can alter microstructure and residual stress. A component's tolerances, surface finish and defect population therefore depend on the production route. Reproducibility requires measuring variation across parts and relating it to the required function. Material selection and process selection are coupled because a good nominal property is of little use if the required geometry cannot be made consistently.

Material selection chooses materials by matching their properties and processing routes to a component's requirements. First exclude candidates violating constraints such as operating temperature, corrosion resistance or minimum stiffness, then compare a performance objective such as mass or cost. A tension member carrying force $F$ over length $L$ needs area at least $F/{\sigma }_{\mathrm{allow}}$, giving mass at least $FL\rho /{\sigma }_{\mathrm{allow}}$. Thus specific strength is relevant for this strength-limited case. A stiffness-limited beam can instead have a different material performance index, so there is no universally best lightweight material independent of geometry and loading.

Michael Ashby develops methods for material selection in engineering design. Materials selection charts compare properties across families of materials, while material performance index values express what a particular design objective rewards. This connects a choice of material to a component's function and constraints, such as low mass with adequate stiffness. His institutional profile identifies materials and design as central themes of his work.^[ref]