Materials generally exhibit four basic viscosity profiles: Newtonian, pseudoplastic, dilatant, and thixotropic.

Newtonian fluids are considered “ideal” because their viscosity remains constant regardless of the applied shear or stress.  In contrast, pseudoplastic materials show shear-thinning behavior, meaning their viscosity decreases as shear increases, while dilatant materials exhibit shear-thickening, where viscosity increases under higher shear.

Thixotropic materials add another dimension as they are both shear and time dependent.  The animation on the right exhibits how the viscosity decreases under shear but takes time to recover once the stress is removed.  This delayed recovery can be beneficial in applications like coatings, helping improve flow and leveling while minimizing sag.