The reason why paper will flatten when it is dried in the refrigerator is because the main component of paper is fiber, and the hydroxyl groups of fiber molecules are hydrophilic. Water enters the gap between fibers, which expands the space between fibers and causes the moisture absorption part to expand and distort locally. When water evaporates, it starts from both ends of the fiber. If drying is accelerated, the water molecules will leave quickly, and the fibers will harden quickly, so the opened gaps cannot be recovered, so the paper will wrinkle after drying. When the fiber structure of paper changes, the changes of texture and shape are inevitable. In the cold room of the refrigerator, it can effectively prevent the rapid evaporation of water, so that the paper fiber has enough time to restore its original state. After the wet paper is frozen, the water directly sublimates from solid to gas, and the air drying time is basically the same, so the paper is relatively flat after drying.