4809.20 - Self-copy paper:

HTS Code 4809.20 specifically classifies "Self-copy paper." This category encompasses papers designed to duplicate information written or printed on them without the need for carbon paper. These papers typically rely on microencapsulated dye or chemical coatings on one side, which rupture upon pressure, transferring the ink or image to a receiving layer on the sheet below.

This category is distinguished from its sibling, 4809.90 "Other," by its specific function as a self-duplicating medium. While 4809.90 would include other types of copying or transfer papers not fitting the self-copy description, 4809.20 is exclusively for papers that produce a duplicate image through inherent chemical or physical reactions triggered by pressure.

Within HTS 4809.20, further subcategories exist to refine the classification. 4809.20.20.00 covers "Writing paper" that incorporates self-copying properties, implying its primary intended use is for handwritten duplication. The broader category of 4809.20.40.00, "Other," captures self-copy papers not specifically designated for writing, which could include those used for printing or other applications where the self-copying functionality is paramount.