Change reversibly due to a change in the surroundings or environment such as light or temperature
Thermochromatic
change colour due to temperature
Photochromatic
change due to light intensity
Hydrogels
Polymers that can absorb larger amounts of liquid and expand to many times their normal volume. They can expel large amounts of liquids depending on the pH and temperature
Shape memory materials/alloys
Can be shaped and reshaped and then return to their original shape when heated
