When a material changes it shape/volume it is mostly due to small changes. For exampel piezoelectric ceramics can grow or shrink very litle, around 0.1%. Shape memory alloys can change up to 8%. And there are also different kinds of waxes that changes 3-4%, though the waxes are not seen as smart materials.

Research is also made in changing the thickness in fabrics to modulate the insulation parameter. These reactions are mostly irreversible and therefore not seen as smart material, but some research is also made to make the fibre in the fabric to change position and hence change the thickness of the fabric.

An exception is some "hydrogelic polymers" that can change its volume up to 3 times. A strong limitation to these polymers is that they must have contact with liquid.

At NASAs Jet Propulsion Lab (JPL) in San Diego a research group under Dr Joseph Bar-Cohen has been working since 1998 with concept called Electro Active Polymers (EAP) with an aim to invent an artificial muscle that can be used for the next generation of space explorations. Dr Bar-Cohen has edited a couple of books in the subject and is also hosting an annual international conference in the subject. The progress in this research filed is currently very active and an interational network of reserachers has emerged.

Piezoelectric polymers

When a piezoelectric material's molecular lattice is squeezed or stretched, it generates an electrical charge.

Magnetostrictors

Magnetic fields as driving forces...

Auxetic materials

Stretch the materials and it grows fatter. Pull them in one direction and they expand in another as well.

Military material that expands

Isolating textiles...

Darpa

The Defense Advanced Research Projects Agency (DARPA) is the central research and development organization for the Department of Defense (DoD) in USA. Articles about piezoelectric materials, shape memory alloys and more.

Shape memory alloys

Metall that changes shape whith temperature.

Artificial muscles

Artificial muscles that are similar to our muscles.

Menotic materials

"Medical materials" that integrate with host tissue.

Hydrogelic polymers

(Wax)