Cellulose ethers, including HEC, HEMC, CMC, and HPMC, are essential additives in water-based coatings. They primarily function as thickeners and rheology modifiers, providing excellent sag resistance and application properties. HPMC and HEC are most common, offering superior water retention, which extends open time and improves leveling. CMC is often used in lower-cost formulations. All contribute to film formation stability, pigment suspension, and overall coating performance.