(1) Whiteness: Although whiteness does not determine whether HPMC is easy to use, and if whitening agents are added during the manufacturing process, it can affect the product’s quality. However, most high-quality products tend to have good whiteness.

(2) Fineness: HPMC typically comes in fineness grades of 80 mesh and 100 mesh, with 120 mesh being less common.

(3) Transmittance: Place hydroxypropyl methylcellulose (HPMC) into water and form a transparent colloid. Then, observe its transmittance—the higher the transmittance, the better, indicating fewer insoluble particles present. Vertical reactors generally exhibit superior transmittance, while horizontal reactors tend to perform slightly worse. However, this does not necessarily mean that products from vertical reactors are of higher quality than those from horizontal reactors; many other factors also influence product quality.

(4) Specific Gravity: The higher the specific gravity, the heavier and better the product tends to be. A higher specific gravity usually indicates a higher content of hydroxypropyl groups; and a higher hydroxypropyl content generally results in better water-retention performance.