in inter-atomic spacing resulting from strain affect the bandgaps, making it easier (or harder depending on the material and strain) for electrons to be raised into the conduction band. This results in a change in resistivity of the material. Within a certain range of strain this relationship is linear, so that the piezoresistive coefficient
:where
:∂ρ = Change in resistivity
:ρ = Original resistivity
:ε = Strainare constant.

Piezoresistivity in metals