Sponge trays have been very popular since they came out, and their market share has been increasing year by year, but there are not many people who can correctly distinguish their quality and scope of use.
The use of sponge is measured in accordance with the "ppi (sponge quality)" indicator. PPi refers to the sponge per square inch [par per inch]. The index range of the sponge plate is 40-90ppi, the higher the PPi index, the softer the sponge; the lower the PPi index, the harder the sponge. Therefore, sponge discs are divided into three types: grinding discs, polishing discs and reduction discs, which are often said to be coarse, medium and fine. Generally speaking, the grinding disc should be 40-50PPi, the polishing disc should be between 60-80PPi, and the PPi index of the reduction disc is 90PPi. Therefore, the disadvantage of the sponge disc is that the cutting force is weaker than that of the wool polishing disc. The advantage is that it is not easy to leave whirlpools. It is suitable for middle polishing and restoration, and has less damage to the paint surface.