Devices for use with a mammography unit and for patient comfort comprise an x-ray transparent compressible material and a radiopaque identifier which imparts information onto a mammogram about physical and other characteristics of the material that affect image quality. The identifier is generally affixed to the material, and, for example, it can be sealed within the material. The material substantially conforms to patient contact surfaces of a cassette holder (bucky) or a compression paddle and, in one example, contains openings to accommodate passage of a cassette therethrough. The devices are for single use or reusable. X-ray transparent disposable covers used over the devices can also have a radiopaque identifier keyed to desired information about, for example, physical and other characteristics of the material that affect image quality. All information appears away from the breast image.