While tank containers are known for transporting liquid products, ISO tank containers are built based on ISO standards (International Organization for Standardization) and are designed to carry liquids in bulk, both hazardous and non-hazardous. These containers are made of stainless steel and are surrounded by various types of protective layers. Based on the cargo type, different skins can be used. The container has a manhole on the top along with at least one valve and another valve on the bottom. They are shaped like a cylinder. Since ISO tanks are built based on ISO standards, the frame which the tank sits in measures about 6 meters long, 2.4 meters wide and between 2.4–2.5 meters high and vary in size and type and can carry between 21,000 and 40,000 liters of liquid.