A visual wear indicator is disclosed capable of giving a visual indication
of the degree of wear on an athletic or other type of shoe. In general,
the visual wear indicator may operate by having two different colored
regions, each having a viscosity which varies a function of pressure.
Before pressure is applied, the boundary between the two regions is
clear. However, over time, as the midsole and/or outer sole of the shoe
wear away, the pressure exerted on the visual wear indicator increases
during activity. As the pressure increases, the viscosity of the regions
eventually decreases. When the viscosity decreases, the regions bleed
together, and the boundary between the regions becomes less clear. The
degree of mixture between the regions may be calibrated to give a clear
visual indication of when the shoe has worn down to the point where the
shoe is unable to provide a desired level of support and stress
absorption.