Flexible magnets with adhesive have a release liner that you pull back to expose the adhesive. You can apply a variety of substrates and objects to the adhesive and convert to a magnet. Great for auto application, arts & crafts and much more. "Mil" is a magnet industry term that stands for thousandth of an inch. The higher the mil the thicker and stronger the magnet. A 30 mil magnet has about 85 lbs. pull per sq. foot.