Foam

Foam is a material in which gas-filled pores are distributed through a solid or liquid matrix. Its properties depend on pore structure and the surrounding matrix.

Cellular solid: A solid made of interconnected or isolated cells separated by solid walls or struts. Solid foams are cellular solids whose cell geometry governs stiffness and strength.
Foaming: The process of introducing or generating gas bubbles within a liquid or polymerizing material. Foaming creates the dispersed gas phase that gives foam its characteristic structure.
Polyurethane foam: A cellular polymer produced by reacting polyols with isocyanates while generating gas. Its tunable softness and density make it common in cushions and insulation.
Aerogel: A highly porous solid in which a continuous nanoscale network surrounds a gas-filled pore space. Aerogels are exceptionally porous, but their pores are far finer than ordinary foam cells.
Gas bubble: A pocket of gas enclosed by a liquid or solid boundary. Bubbles form the gas-filled pores that define foam.
Coalescence: The merging of droplets or bubbles when the separating film ruptures. Bubble coalescence enlarges pores and weakens a foam's uniform structure.
Metal foam: A porous metal containing gas-filled cells within a continuous metallic framework. It combines low mass with energy absorption and heat-transfer capabilities.
Sponge: A porous material with interconnected voids that can absorb and release fluids. Many sponges contain connected pores, unlike foams with predominantly enclosed cells.
Liquid film: A thin liquid layer separating two gas regions or other phases. In liquid foams, films between bubbles help hold the structure together.
Ostwald ripening: The growth of larger dispersed domains at the expense of smaller ones through molecular transport. Gas transfer between bubbles can coarsen foam even without bubbles touching.

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