When purchasing HEC, the most critical factor is viscosity, typically measured in a 1% or 2% aqueous solution using a Brookfield viscometer. You must specify the required molar substitution (MS) levels, as this determines the biostability and water retention capabilities. For paint and coating industries, prioritize delayed-solubility (surface-treated) grades to prevent lumping during the mixing process. Additionally, verify the purity level (ash content); high-quality industrial HEC should generally have an ash content below 5% to ensure chemical stability.