The use of material design to overcome time-dependent material deformation resulting in loss of sealing effectiveness of elastomeric seals was considered. O-ring sections with different stress-strain behavior in different regions of the section were studied. Experimentally validated finite element models were used to characterize the strain energy density distribution and seal-housing contact pressure for various section designs. The design rules extracted from experimental and numerical studies indicate that o-ring sections with lower elastic modulus, softening material located at regions of high strain energy will result in slower growth of permanent seal deformation and so improved seal performance over time. O-ring sections based on this material design were evaluated numerically and improved seal life predicted.