Synthetic rubber under 4002 is the base polymer before compounding agents are added. Once that polymer is mixed with carbon black, silica, vulcanizing agents, or other compounding ingredients, the resulting blend classifies under 4005 as compounded rubber, provided it has not yet been vulcanized.

Yes. Compounds in plate, sheet, or strip form (other than carbon-black or silica types) fall under 400591, while those in other primary forms such as pellets, granules, or crumbs fall under 400599. Carbon-black and silica compounds have their own dedicated subheading (400510) regardless of form.