Papermaking is one of the four great inventions in China. It was invented in the Western Han Dynasty and improved in the Eastern Han Dynasty. China is the first country in the world to raise silkworms and weave silk. In ancient China, the working people of the ancient times drew silk from silkworm cocoons, and the remaining cocoons and diseased cocoons were made of silk cotton by bleaching. After the drifting is completed, there will be some residue left on the mat. When there are many times of flocculation, the residual flocs on the mat will accumulate into a layer of fibrous flakes, which can be peeled off after drying and can be used for writing. There are not many by-products of this kind of bleaching, and it is called Hejia or Fangxu in ancient books.