Oat flakes, also known as rolled oats, are made of oats and they have many different sizes, thicknesses and other characteristics depending on the size of oat groats passed between the rolls. Typically, the three sizes of steel cut oats are used to make instant, baby and quick rolled oats, whereas whole oat groats are used to make regular, medium and thick rolled oats. Oat flakes range in thickness from 0.36 mm to 1.00 mm.