Single layer folding in simple shear

► Folds are modelled in simple- and pure shear to very high strain. ► Amplitude and wavelength do not suffice to distinguish simple- and pure shear. ► Foliation refraction patterns do differ between simple- and pure-shear folds. ► Non-linearity of rheology increases effective viscosity contrast. ► The arc-length method can significantly underestimate the true amount of strain.