Adhesive PVC cards are made so that you can peel off the back and adhere your card to your Access Card.
Some Corporations or Businesses use Clamshell Access Cards and most ID Card printers can't print on clamshell ID cards. Adhesive PVC Cards can be ran through your ID Card printer and then you can peel off the liner and adhere directly to your Access Card. Adhesive cards come with either a paper back liner or a mylar back liner.