Spray paint is paint that comes in a sealed, pressurized container and is released in an aerosol spray when a valve button is depressed. The propellant is what the container of pressurized gas is called. When the pressure holding the gas is released through the valve, the aerosol paint releases as a fine spray. Aerosol painting is one form of spray painting; it leaves a smooth, even coat, unlike many traditional rolled and brushed paints. Aerosol primer can be applied directly to bare metal and many plastics.