Aerosol cans are made in various ways, normally from metals that can safely contain pressurized liquids and gases. The tinplate is wrapped into a cylinder that has a top and a bottom welded on to ensure the can is complete just inside the can, the valve is tightly closed. A spring holds the valve tightly in place. The can is perfectly and safely sealed. No product or propellant can escape. Press down on the button and everything changes! Pushing down on the button pushes the valve down too. Under the valve, the spring is tightly compressed. The pressurized product and propellant escape through an opening at the top of the valve. As they leave the nozzle, the product and propellant form an aerosol (mist spray).