Multi-layer cell factory is the adherent cells' ideal choice for industrial mass production, laboratory operations, and large-scale cell cultures. The cell factory is a bioreactor system used for high-density cell culture in an adherent culture. Adherent culture is a technique used to culture cells that require a surface to grow on, such as stem cells and many types of animal cells. The cell factory consists of multiple layers of stacked polystyrene plates, each with a surface area of up to several thousand square centimeters. The plates are coated with a layer of extracellular matrix protein to support cell adhesion and growth. The cell factory is designed to optimize cell growth and productivity by providing a controlled environment for the cells. The system is equipped with a quick-switching sealing lid that can switch between airtight and air-permeable states to regulate the dissolved oxygen and exhaust gas levels during different stages of cell growth. The double large mouth design of the cell factory allows for easy liquid filling and harvesting, and the system is designed to minimize air bubble formation to facilitate gas exchange.