A foam is a substance that is formed by trapping pockets of gas in a liquid or solid. A bath sponge and the head on a glass of beer are examples of foams. In most foams, the volume of gas is large, with thin films of liquid or solid separating the regions of gas.

An important division of solid foams is into closed-cell foams and open-cell foams. In a closed-cell foam, the gas forms discrete pockets, each completely surrounded by the solid material. In an open-cell foam, the gas pockets connect with each other. A bath sponge is an example of an open-cell foam: water can easily flow through the entire structure, displacing the air. A camping mat is an example of a closed-cell foam: the gas pockets are sealed from each other, and so the mat cannot soak up water.

Foams are examples of dispersed media. In general, gas is present in large amount so it will be divided in gas bubbles of many different sizes (the material is polydisperse) separated by liquid regions which may form films, thinner and thinner when the liquid phase is drained out of the system films. When the principal scale is small, i.e. for a very fine foam, this dispersed medium can be considered as a type of colloid.

The term foam may also refer to anything that is analogous to such a foam, such as quantum foam, polyurethane foam (foam rubber), XPS foam, Polystyrene, phenolic, or many other manufactured foams. This is not the purpose of this page.

Read more about Foam:  Structure of Foams, Foaming and Foam Stability, Experiments and Characterizations, Defoaming, Speed of Sound, Gallery, Foam Scales and Properties

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Famous quotes containing the word foam:

    Only the white, tremendous foam of the street has any importance,
    The new white flowers that are beginning to shoot up about now.
    John Ashbery (b. 1927)

    “To dine!” she shrieked in dragon-wrath.
    “To swallow wines all foam and froth!
    To simper at a table-cloth!”
    Say, can thy noble spirit stoop
    To join the gormandising troop
    Who find solace in the soup?
    Lewis Carroll [Charles Lutwidge Dodgson] (1832–1898)

    Yet ere I can say where—the chariot hath
    Passed over them—nor other trace I find
    But as of foam after the ocean’s wrath
    Percy Bysshe Shelley (1792–1822)