Raw silk is made of several cocoon filaments hugging each other and glued by sericin. It contains about 80% silk protein and about 20% sericin. Raw silk is a porous fiber, with a void capacity of about 35% and a maximum diameter of 1 �¼ m. As the cross section of the cocoon silk is triangular, and the cocoon silk is arranged in an irregular conical helix, and is fixed in the raw silk in a slightly tortuous state, the cross section shape of the raw silk is approximate to an ellipse (see figure). The cross section of raw silk with a size of 22 denier is about 60~70 m in long diameter and 40~50 m in short diameter.