1 gallon of ChemWorld Inhibited Propylene Glycol. ChemWorld Boiler Antifreeze Concentrate is a 95% inhibited Propylene Glycol. It is a low hazard, propylene glycol based heat transfer fluid concentrate for use in closed water systems both hot and cold. The corrosion inhibitor package provides an effective combination of inhibitors for steel, cast iron, copper, cupric alloys, and aluminum. 30% of Boiler Antifreeze will provide freeze protection until 5 F, 40% will provide protection until -20 F and 50% will provide protection until -35 F.