Aluminum foil is produced by rolling aluminum slabs cast from molten aluminum in a rolling mill to the desired thickness. To maintain a constant thickness, a technician monitors the rolling mill sensors to ensure the pressure on the slab is correct. Sensors are able to tell the technician if the pressure is too great or not enough and then the technician can adjust the rollers to apply more or less pressure. It is then coiled and sent to the cold rolling mill. To avoid breakage because of the thinness, the foil is doubled in the cold rolling mill and the rolled to the desired thickness. Aluminum foil provides a complete barrier to light, oxygen, moisture and bacteria. For this reason, foil is used extensively in food and pharmaceutical packaging. It is also used to make aseptic packaging that enables storage of perishable goods without refrigeration.