The composition of sea foam is generally a mixture of decomposed organic materials, including zooplankton, phytoplankton, algae (including diatoms), bacteria, fungi, protozoans, and vascular plant detritus, though each occurrence of sea foam varies in its specific contents. In some areas, sea foam is found to be made up of primarily protein, dominant in both fresh and old foam, as well as lipids and carbohydrates. The high protein and low carbohydrate concentration suggest that sugars originally present in the surrounding mucilage created by algae or plant matter has been quickly consumed by bacteria. Additional research has shown that a small fraction of the dry weight in sea foam is organic carbon, which contains phenolics, sugars, amino sugars, and amino acids. In the Bay of Fundy, high mortality rates of an abundant tube-dwelling amphipod (Corophium volutator) by natural die-offs as well as predation by migrating seabirds contributed to amino sugars released in the surrounding environment and thus, in sea foam.
The organic matter in sea foam has been found to increase dramatically during phytoplankton blooms in the area. Some research has shown very high concentrations of microplankton in sea foam, with significantly higher numbers of autotrophic phytoplankton than heterotrophs Some foams are particularly rich in their diatom population which can make up the majority of the microalgal biomass in some cases. A diversity of bacteria is also present in sea foam; old foam tends to have a higher density of bacteria. One study found that 95% of sea foam bacteria were rod-shaped, while the surrounding surface water contained mostly coccoid-form bacteria and only 5% - 10% rod-shaped bacteria. There is also seasonal variability of sea foam composition; in some regions there is a seasonal occurrence of pollen in sea foam which can alter its chemistry.  Though foam is not inherently toxic, it may contain high concentrations of contaminants. Foam bubbles can be coated with or contain these materials which can include petroleum compounds, pesticides, and herbicides.