A mini card has a size smaller than a card that conforms to established standards, and includes a hole for attachment to a key ring or other external device. Increased durability is provided by means of a substrate that includes a core made of PVC material, sandwiched between two durable layers of polyester material. Printing on these layers is protected by transparent overlay layers made of PVC. The durability of the card is measured by means of a test procedure in which random multi-dimensional motion is imparted to an assembly of the card and an attached weight. The durability is quantitatively indicated by the amount of elapsed time until the weight becomes separated from the card while undergoing the vibrational movement.