How does a Polymer Capacitance Humidty Sensor work technically ?

Answer 1

Water molecules pass through a permiable top layer. This top layer is conductive and serves as one plate of a capacitor with the polymer serving as the dielectric.

Water molecules entering the dielectric layer change its dielectric constant. You may also think of it as the conductive water molecules allow the charge on the top plate to travel closer to the bottom plate. THis effectively shrinks the dielectric thickness bringing the plates closer and raising capacitance. Your choice which ever helps you visualize it. Add moisture and capacitance goes up....