Foam fluxers are installed in wave soldering systems and are used to apply foamed flux to the full area of a passing printed circuit board. To generate the foam, compressed air is pressed through a synthetic or ceramic pipe with micro pores (termed aerator), which is submerged in the liquid flux and placed inside an upwardly tapered nozzle. The top portion of the nozzle is above the liquid. Through the fine pored air bubbles leaving the aerator stone, the flux is being foamed up and flows over the top of the nozzle. The foam head contacts the underside of the board, thereby wetting the board and applying the flux. A drawback of foam fluxers is the evaporation of the alcohol, which is used as a thinner, which causes the solid content of the flux to change over time. In addition, flux is hygroscopic and will absorb moisture from the environment. Modern alternatives to foam fluxers are spray fluxer, where it is easier to control the amount of flux applied as well as being more precise.