Bi-material strips constructed from components having different mechanical properties, in particular different Young’s moduli and/or Poisson’s ratio, are shown to curve when subjected to changes in the external hydrostatic pressure in a similar manner that such strips curve when subjected to a change in temperature when the component materials have different coefficients of thermal expansion. This behaviour will be particularly pronounced if the material having the lower Young’s modulus also exhibits a negative Poisson’s ratio (auxetic).