Vanishing foam

Vanishing spray, also known as vanishing foam, is a substance applied to an association football pitch in order to provide a temporary visual marker. Its use in football is not regulated by the Laws of the Game, authorisation being in the hands of the governing body of a match, league, or tournament. In football, referees use the spray to enforce the rules as to the minimum distance that members of the opposing team can come close to the ball during a free kick, as well as the spot from which the kick is taken.

Used mainly at the highest levels of competition, vanishing spray is said to help prevent unnecessary delays by preventing the defensive team from encroaching closer than the mandated 10 yards (9.1 m) from the ball during a free kick, and also by preventing the attacking team from illegally moving the ball from the spot where the referee awarded the kick.

Vanishing spray is applied from an aerosol can carried by the referee in a holster secured to their shorts. The referee has full discretion on whether or not to use vanishing spray, and opponents are required to retreat 10 yards from the spot of a free kick regardless of whether vanishing spray is used (unless the team awarded the kick elects to take a "quick" free kick with opponents still within 10 yards). It is generally only used when a free kick is awarded where a goal-scoring attempt is highly likely to develop (e.g. it is usually not used when a team is awarded a free kick in its own half of the pitch). When the referee chooses to use vanishing spray, he or she will usually mark the spot of the ball, then pace 10 yards in the direction of the attack, then spray a line marking that distance. Finally, the referee will indicate for the free kick to be taken, usually by blowing the whistle. The marks disappear after about one minute.

The can contains water (~80%), butane gas (~17%), surfactant (~1%), and other ingredients including vegetable oil (~2%). The liquefied butane expands when the product is ejected from the can. The butane evaporates instantly, forming bubbles of gas in the water/surfactant mixture. The surfactant(s) cause the bubbles to have stability and hence a gas-in-liquid colloid (foam) forms. The bubbles eventually collapse and the foam disappears, leaving only water and surfactant residue on the ground. More technical details can be found in the US patent applications for two of the commercial products available: Spuni (2001) and 9-15 (2010).

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