Standard QB/T 4581-2013 specifies technical requirements, test methods, inspection rules and marks, Encasement, transportation and storage requirements for retanning protein fillers used in tanning. The standard applies to retanning protein fillers used in the tanning industry and covers the requirements of physical performance, chemical performance and impact on the mass of the finished leather product of the filler. The standard details the inspection items of filler composition, Appearance mass, Moisture content, ph value, etc., and specifies the corresponding test methods and evaluation standards to ensure the mass stability and safety performance of the filler. Manufacturers and users can use this standard to accurately evaluate and select retanning protein fillers to ensure their effective application in the tanning process and the mass and durability of finished leather products.