Contrary to what it sounds like, “flex fuel” is not a powdered fitness supplement bodybuilders buy at GNC to amp up their clang-and-bang workouts. Flex fuel generally refers to a type of vehicle that is flexible enough to run on automotive fuel with a heavy blend of ethanol (a grain alcohol made from plant material) and gasoline, on straight gasoline or on any mixture thereof. You may also hear the fuel itself referred to as flex fuel, but we’re not on board with that practice for reasons touched on below.
Related: Another Reason Your Mileage May Vary (for the Worse): Ethanol