This is one of the most common questions we get asked. There are two basic methods for accomplishing this: 1) print directly onto a proximity card or 2) print onto a label or adhesive-backed card which you then peel-and-apply to a clamshell or other proximity card.
Option #1: In order to print directly onto an HID proximity card, you will need to use cards that have a CR-80 form factor, such as the HID 1386 card or the HID 1586 card. CR-80 refers to the card dimension; a CR-80 card measures 3.375” x 2.125” (the same as most credit cards) while a CR-79 card is slightly smaller measuring 3.303” x 2.051”. The difference between the 1386 card and the 1586 card is the card material; the 1586 card uses composite materials that can withstand significant heat making them ideal for use with a re-transfer card printer (e.g. the Zebra ZXP Series 9 card printer) or when the cards will be laminated. For card printers that use dye-sublimation technology, you can use the more common HID 1386 card.
Option #2: Print on to a label or adhesive card which you then peel-and-apply to a HID 1326 clamshell card. From our experience, we recommend 24-mil, Mylar-backed adhesive cards like Zebra P/N 104523-010 or Fargo P/N 082267. 
There are many other Mylar-backed adhesive cards but we recommend these two because:
- These are both CR-80 sized cards with a 24 mil thickness so they can be used in a wide range of printers. CR-79 sized labels, like the HID 1324 printable clamshell labels, can NOT be used in some ID card printers. Similarly, the 24-mil thickness of these cards (10 mil card with 14 mil Mylar backing) makes them more suitable for a broad range of printers as compared to 10-mil paper-backed labels. Additionally, the extra card thickness of these 24 mil cards make them less susceptible to card jamming when printing. In either case, you should verify that your card printer supports the card/label size (CR-79 or CR-80) and thickness (10 or 24 mil) you choose. The Zebra Knowledge Base highlights some of the advantages of 24 mil cards in this article.
- They use a Mylar backing which is better than a paper backing as the latter can be slippery and cause problems with some card printers (resulting in ribbon breakage). For more information, you can refer to this article from the Zebra knowledge base Adhesive Style Card Used with a Zebra Card Printer.
The advantage of printing directly onto a card is greater security as the photo ID (adhesive back card) cannot be removed. The disadvantage of printing directly onto a card is that these cards are more expensive and cannot be re-used.
