Fire fighting foam is a collection of bubbles, formed by the mixing of water, foam concentrate (or foam compound) and air. The mixture of water and foam concentrate is called foam solution with water being 97% to 94% of the mixture, while 3% to 6% is the foam concentrate. The foam solution is mixed with air, the ratio of which can vary from 1:2 to over 1:1000 depending upon the type of foam equipment used and its application.
Fire fighting foam being lighter than water can float on flammable liquid (while water sinks below the liquid surface), hence is very effective in fighting flammable liquid (Class B) fires. It can also be used to cover flammable liquid spills and prevent fires. With higher expansion ratios (more than 1:500) it is also used to fight Class A fires, where it results in minimal water damage.