Payment cards have evolved from embossed paper tokens in the 1920s to today’s multilayered, data-rich, machine-readable artefacts. Their outward appearance—the printed design, dimension, embossing and embedded electronics—hides a precisely standardised internal logic. At the visual level, cards must be instantly recognisable, brand-aligned and resistant to wear; at the data level, the primary account number (PAN) and ancillary codes must satisfy global routing, security and regulatory requirements. This article integrates research from materials engineering, digital security and payment-network governance to explain (1) how the surface aesthetics and physical composition of cards are engineered, (2) how the numbering system encodes issuer, industry and account identifiers, and (3) how both layers interact to satisfy durability, interoperability and fraud-mitigation goals.