1. The mineral water bottle is made of plastic, which can be easily molded into a round bottle. Round is the most material-saving structure with the highest strength under the same volume.
2. Milk carton is a patent of tetra pak Brick, which is made of paper and aluminum foil. It is more difficult to process into a circle, but it is easier to make it into a square. Its cost is higher than the round bottle of plastic products.