Both raw flax (harvested stalks with no processing) and retted flax (stalks that have undergone retting to begin fiber separation) are covered by the single 10-digit line 5301100000—there is no tariff distinction between them at this stage. The classification difference arises at the next processing step: broken or scutched flax moves to heading 530121, and hackled or otherwise processed (but not spun) flax moves to 530129.

Belgium's Flanders region has centuries of linen-industry infrastructure, including retting facilities and trading houses that aggregate flax from broader European growing areas. Belgian suppliers often act as re-exporters or processors of flax grown in France and the Netherlands, which explains the country's prominence in US import data even though raw flax cultivation is geographically distributed across northwestern Europe.