D3O belongs to “expandable foam” material, and it is a shock resistance single material composed of "smart molecules" component (chemically combined by viscose fluid and a polymer). Under normal conditions, its molecules are moved freely, and the material is soft and flexible. Its appearance looks like elastic plasticine which is favored by children. Once it is suffered violent impact or squeezing, it is interlocked immediately among molecules, tightened and hardened rapidly to digest external force and form a protective layer. When the external force is disappeared, the material is recovered to initial loose and flexible state.

Knead D3O into a shape randomly and cover it on the finger surface. Then, use a mallet to knock on the finger which is covered by D3O violently, and the result shows that there is no uncomfortable feeling for the finger of the testee.