When we mention “density”, we would immediately bring into mind the famous scientist: Archimedes. He applied the water displacement method and buoyancy method, through which we know the basic concept that “density” equals to “weight” divided by “volume”. However, as the demand of the market, the new composite materials have been successively developed, displacing the traditional manufacturing method. As the replacement of the materials, the measuring methods of materials and products have also changed. According to the ASTM, the materials and products are divided into: 1、Non-absorbent or porous materials and products containing less than 2% porosity . 2、Absorbent or porous materials and products containing more than 2% porosity. Therefore, there are differe..