Metal foam is a foam — gas bubble-filled substance — made out of metal, frequently aluminum. Metal foam comes in two varieties, closed-cell foam, with sealed pores, and open-cell foam, with open pores. Metal foams have a very high porosity, where 75-95% of the volume of the material is empty, filled by air or hydrogen. Metal foams retain many of the characteristics of the metal used to produce them, such as non-flammability. On the other hand, metal foams are less conductive than solid metal, and are substantially weaker, though rarely weaker than wood. Metal foams are easily recyclable back into the original metal, making them more reusable than polymer foams.

Metal foam is sometimes considered a subset of cellular metallic materials in general, which also includes "metal sponges," though often the term "metal foams" is used interchangeably with all cellular metallic materials. Several categories of cellular metallic materials are distinguished, including cellular metal (metal foam with internal cells, usually closed), porous metal (with closed, smoothly curved voids (pores) rather than jagged or open voids), metallic foams (special cases of porous metals, created by bubbling gas through liquid metal and then letting it solidify), and metal sponges, which is essentially open-cell foam where the entire space of voids is interconnected. These categories are not mutually exclusive, and there are some substances that straddle multiple categories. For instance, a foam with breaks between the cell walls may be on the edge of a metal foam and a metal sponge.

Many metal foams are created by introducing air bubbles into molten metal. Making a foam out of molten metal is not easy, and the material is accordingly expensive. A foaming agent such as powdered titanium hydride, which decomposes into titanium and hydrogen at high temperatures, must be used. Metal foam is a specialty material, used for aerospace, heat exchangers, and other high-performance applications. Because metal foam is stiff and light, it has often been proposed as a futuristic structural material, though it has not yet seriously been used as one. Some commercial metal foams include M-Pore, Porvair, Duocel, Metal Foam Korea, Metafoam and Recemat. The pores in metal foams are usually between 1-8 mm in diameter, but some specialty foams have pores so small they are invisible to the naked eye.

"Metal foam" or "metallic foam" has become a very popular term which is nowadays used for almost any kind of metallic material which contains voids. It might be useful to distinguish various expressions:

cellular metal: space is divided into distinct cells. The boundaries of these cells are made of solid metal, the interior are voids. Ideally, the individual cells are all separated from each other by metal but often this restriction is relaxed porous metal: the metal contains a multitude of pores, i.e. closed, curved gas voids with a smooth surface.

metal(lic) foam: foams are special cases of porous metals. A solid foam originates from a liquid foam in which gas bubbles are finely dispersed in a liquid.

metal sponge: space is filled by pieces of metal that form a continuous network and co-exist with a network of empty space which is also interconnected.

Related data
Porosity:  1—120 PPI (pores per inch)
Density:  0.15~0.45g/cm3
Pores:  90%—98%

Feature:
1. the excellent mechanical property and processability;
2. the extraordinary electricity and heat conductivity;
3. the massive and intricate lattice- inner structure
4. the super ability of corrosion resistance, superior tensile strength, favorable ductility;
5. the magnificent electromagnetic shielding ability.

Application:
1. Filtration materials of air/oil/smoke etc;
2. Heat elimination and exchange material for electronic components, such as CPU, Display Card and LED;
3. Noise absorption and vibration reduction material;
4. Electrode material for batteries, such as lithium ion battery, fuel cell, nickel-zinc battery and so on; 5. Electromagnetic shielding materials;
6. Decoration materials for the construction;
7. Various primary filters;
8. Catalyst carrier.

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