Thixotropy is a rheological property of certain materials characterized by a decrease in viscosity over time when subjected to mechanical stress (such as stirring or shaking), followed by a gradual recovery of viscosity when left at rest. In simple terms, a thixotropic fluid becomes temporarily more fluid when agitated and returns to a thicker state once the agitation stops.

This behavior is typical of non-Newtonian fluids, meaning their viscosity is not constant but depends on external conditions. Unlike pseudoplastic fluids (which become less viscous with increasing shear rate), thixotropic materials exhibit a time-dependent response.

A common example is yogurt: it appears solid in the container but turns creamy when stirred. Other examples include gels, drilling muds, paints, and some types of inks.

Thixotropy is important in many industrial applications because it allows for easy handling or application (due to temporary fluidity) while maintaining stability at rest (thanks to the return of thickness). This behavior is analyzed using rheological tests that measure how viscosity evolves over time under stress.