This sounds like an "electroactive polymer." there are some squishy tapes made by 3m that incidentally have this property out of the box. Make a spot of conduct

This sounds like an "electroactive polymer." there are some squishy tapes made by 3m that incidentally have this property out of the box. Make a spot of conductive carbon paint on each side, apply a few kV, and watch the spots double in area as the electrostatic forces squish the material.