Diesel Exhaust Fluid (DEF) is injected into the exhaust system of modern diesel engines. Containing no chemical additives, DEF is used to break down nitrogen oxide into water vapor. Although beneficial to the environment, diesel exhaust fluid will freeze at 12°F. Bartelt Insulation's DEFender™ was designed to insulate diesel pumps containing DEF to prevent the fluid from freezing. Our product has proven to be an effective and cost-efficient solution to the problems that arise when DEF is exposed to cold temperatures.