Both silicone fluids (oils) and uncured silicone gums or resins fall under heading 3910 when in primary forms, because the heading captures the polymer before it is fabricated into a finished article. Once a silicone is vulcanized or formed into a shaped article, it may shift to a different chapter. The key test is whether the material retains the character of a primary-form polymer rather than a finished product.

Because global silicone polymer production is dominated by a small number of integrated manufacturers, supply disruptions can affect multiple downstream industries simultaneously. From a classification standpoint, proprietary silicone formulations may include additives that push the product out of heading 3910 and into a more specific heading — importers should review the full composition against the chapter notes.