Foamed

Foamed is an adjective and past participle used to describe a substance that contains a cellular structure formed by gas bubbles dispersed within a liquid or solid. In foams, the gas (usually air) creates many small bubbles that are separated by thin liquid or solid films. Foams can be open-cell, with interconnected bubbles that allow passage through the material, or closed-cell, where each bubble is isolated.

Foaming can occur through several mechanisms. Mechanical foaming involves whipping, stirring, or aeration to introduce gas and create a stable dispersion, as in whipped cream or meringue. Chemical foaming uses a blowing agent that generates gas during processing, common in polyurethane and other polymer foams. Physical foaming involves dissolving gas under pressure and then releasing it, or using volatile liquids that vaporize to form bubbles.

Foams appear in many materials and foods. Polymer foams include polystyrene and polyurethane foams used for insulation and cushioning; metal foams provide lightweight, energy-absorbing structures; ceramic foams serve as refractory or filtration materials. Food foams include whipped toppings, mousses, bread dough (a gas-filled matrix), and beer foam. The properties of a foam—such as density, compressive strength, and thermal or acoustic insulation—depend on cell size, cell wall thickness, and whether the foam is open- or closed-cell.

Stability is a key consideration. Foams can drain, coalesce, or collapse over time, influenced by factors like surface tension, viscosity, surfactants, temperature, and shear. Controlling these factors allows foams to serve roles in packaging, insulation, flotation, filtration, and culinary textures.