From the early 20th century, various types of specially manufactured solid foams came into use. The low density of these foams made them excellent as thermal insulators and flotation devices, and their lightness and compressibility made them ideal as packing materials and stuffings. Some liquid foams, called fire retardant foams, found use in extinguishing fires, especially oil fires.

Foam, in this case meaning "bubbly liquid", is also produced as an often unwanted by-product in the manufacture of various substances. For example, foam is a serious problem in the chemical industry, especially for biochemical processes. Many biological substances, for example proteins, easily create foam on agitation and/or aeration. Foam is a problem because it alters the liquid flow and blocks oxygen transfer from air (therefore preventing microbial respiration in aerobic fermentation processes). For this reason, anti-foaming agents, like silicone oils, are added to prevent these problems. Chemical methods of foam control are not always desired with respect to the problems (i.e. contamination, reduction of mass transfer) they may cause especially in food and pharmaceutical industries where the product quality is of great importance. In order to prevent foam formation in such cases mechanical methods are mostly dominant over chemical ones.

If foaming is desired, a foaming agent may help.

The term sea foam is used to describe the foam that forms on top of seawater from the action of waves. In some ways, leavened bread is a foam, as the yeast causes the bread to rise by producing tiny bubbles of gas in the dough.

The unique property of gas-liquid foams having very high specific surface area are exploited in the chemical processes of froth flotation and foam fractionation.

Structure of foams

Real-life foams are typically disordered and have a variety of bubble sizes. The study of idealised foams is closely linked to the mathematical problems of space-filling and minimal surfaces. The Weaire-Phelan structure is believed to be the best possible (optimal) unit cell of a perfectly ordered foam, while Plateau's laws describe how the soap-films form structures in foams.

Solid foams form an important class of lightweight cellular engineering materials. These foams can be classified into two types based on their pore structure. The first type of foams are called open cell structured foams. These foams contain pores that are connected to each other and form an interconnected network which is relatively soft. The second type of foams do not have interconnected pores and are called closed cell foams. Normally the closed cell foams have higher compressive strength due to their structures. However, closed cell foams are also generally denser, require more material, and consequentially are more expensive to produce. The closed cells can be filled with a specialized gas to provide improved insulation. This is in contradistinction to the open cell foam which will fill with whatever it is surrounded with. If filled with air this could be a relatively good insulator, but if the open cells fill with water, insulation properties would be reduced.