For most liquids, shear thinning is reversible and the liquids will eventually gain their original viscosity when the shearing force is removed. When this recovery process is sufficiently time dependent, the fluid is considered to be thixotropic. Thixotropy is related to the time dependent microstructural rearrangements occurring in a shear thinning fluid following a step change in applied shear. A shear thinning material may be thixotropic but a thixotropic material will always be shear thinning.