Time-dependent viscosity

A thixotropic fluid is one that takes time to attain viscosity equilibrium when introduced to a step change in shear rate.

Certain gels or fluids that are thick (viscous) under static conditions will begin to thin and flow as they are shaken, agitated, or otherwise stressed.

Cytoplasm, synovial fluid (found in joints between some bones), and the ground substance in the human body are all thixotropic, as is semen.

Semi-solid casting processes such as thixomoulding use the thixotropic property of some alloys (mostly light metals, e.g. bismuth) to great advantage.

Thixotropic inks that quickly regain a high viscosity are used in CMYK-type printing processes; this is necessary to protect the structure of the dots for accurate color reproduction.

In addition to obvious potential military applications, rheopectic padding and armor could offer significant advantages over alternative materials currently in use in a wide range of fields from sporting goods and athletic footwear to skydiving and automobile safety.