Self-copy paper (480920) refers specifically to carbonless copy paper — sheets coated with micro-encapsulated dye or reactive clay that produce an image under pressure without carbon interleaving. Subheading 480990 captures other copying or transfer papers that are coated or impregnated with transfer agents but do not function by the carbonless pressure-transfer mechanism, such as certain heat-transfer or spirit-duplicating papers. The functional mechanism of image transfer is the key differentiator.

Thermal paper — coated with a heat-sensitive layer that produces an image when exposed to heat — is generally classified under heading 4811 (paper coated with heat-sensitive substances) rather than 4809, because it does not transfer an image by pressure or chemical contact with another sheet. Importers should confirm the specific coating chemistry and mechanism against the heading texts, as the distinction matters for duty and trade-remedy purposes.