I am modelling soft contact lenses and am currently using an isotropic linear elastic material model in Marc-Mentat. When modelling the inside out turning (flipping) of a soft contact lens I get very good agreement of shapes with laboratory measurements. However, the material model is unable to capture effects of material modulus on the inverted lens shape, i.e. whichever modulus I am using the inverted lens shape doesnt change at all. Does someone know why and has anyone got some experience with modelling hydrogel or silicone hydrogel materials?