4005 - Compounded rubber, unvulcanized, in primary forms or in plates, sheets or strip:

Heading 4005 encompasses compounded rubber that has not undergone vulcanization. This category is specifically for rubber that has been mixed with various additives such as fillers, plasticizers, or reinforcing agents to modify its properties. It covers these compounded rubbers when presented in their basic physical forms, or as plates, sheets, or strip. These are semi-finished rubber products intended for further processing into a wide array of rubber articles.

This heading is distinguished from other rubber headings within Chapter 40 by its focus on *unvulcanized compounded rubber*. For example, it does not include vulcanized rubber (covered elsewhere in Chapter 40) or natural or synthetic rubber in its uncompounded state (like raw latex or basic synthetic rubber polymers). It also differs from headings covering manufactured rubber articles, as 4005 deals with materials that require further manufacturing steps.

Within heading 4005, further subdivisions exist to classify compounded rubber based on its specific composition or presentation. Subheading 4005.10 specifically addresses compounds that have been mixed with carbon black or silica, which are common reinforcing fillers. Other subcategories, such as those covering solutions or dispersions, distinguish between different physical forms in which the compounded rubber might be supplied. A residual "Other" category exists for compounded rubbers not falling into the more specific subdivisions.