'Not thrown' raw silk consists of reeled filaments that have not been subjected to any twisting or throwing process. Once the filaments are twisted—even lightly—the product is classified as thrown silk or silk yarn. The degree of twist and the manufacturing step at which the product is exported determine which heading applies, and mill or producer documentation confirming the processing stage is the key supporting evidence.

Raw silk is graded by filament denier, uniformity, cleanliness, and neatness—characteristics assessed under international standards such as those published by the International Silk Association. Higher grades command significant price premiums and are destined for fine woven fabrics, while lower grades may be used for spun silk or blended products. Buyers should specify grade in purchase contracts and verify grade certification from the exporting mill.