The five indexes are hydroxypropyl content, methoxy content, viscosity, moisture and ash content. The ratio of hydroxypropyl content to methoxy content should be appropriate, the water retention will be good, not just which index is high. Viscosity: When the viscosity is less than 100,000, the water retention increases with the increase of viscosity. However, if the viscosity is more than 100,000, it has little effect on water retention. Another important indicator is the ash content. The popular one can be understood as the impurity of the product. The lower the ash content, the higher the purity, the better the product. The ash content of general products is around 5%, and for better domestic quality, the ash content is around 2-3 percentage points.