Solder flux cleans and prepares surfaces for soldering while preventing oxidation during the soldering process. Solder flux removes material that inhibits adhesion by binding to impurities and lifting them away. Traditional flux is rosin based, although other formulations are available including mild flux and water-soluble flux. Flux thinners are added to flux to make it more viscous and improve coverage. They are often used in reflow soldering or soldering baths.