4008 - Plates, sheets, strip, rods and profile shapes, of vulcanized rubber other than hard rubber:

This HTS category, 4008, encompasses a broad range of vulcanized rubber articles that are not hard rubber. These include items manufactured in the form of plates, sheets, strip, rods, and profile shapes. The defining characteristic is their processing through vulcanization, a chemical process that enhances the rubber's strength, elasticity, and resistance to temperature changes and wear. Examples within this classification could include rubber sheeting used for gaskets or insulation, rubber strips for sealing applications, or extruded rubber rods for various industrial purposes.

Distinguishing this category from its sibling HTS codes is crucial for accurate classification. While other sections within the HTS might cover finished rubber goods like tires (Chapter 40, but typically further specified) or rubber footwear, this heading specifically addresses the semi-finished or basic forms of vulcanized rubber prior to their integration into more complex products. It focuses on the material's form and state of vulcanization rather than a specific end-use application, differentiating it from finished articles where the primary function dictates classification.

Within HTS 4008, a key distinction is made between two primary forms of vulcanized rubber: cellular and noncellular. The subcategory for "Of cellular rubber" covers products that are porous or spongy, containing a multitude of gas-filled cells. This is often achieved through the introduction of blowing agents during the vulcanization process, resulting in materials like foam rubber. Conversely, the "Of noncellular rubber" subcategory encompasses solid, dense vulcanized rubber articles where such cellular structures are absent. This division is based on the fundamental physical structure of the rubber article, impacting its weight, compressibility, and insulating properties.