The only gray card specifically designed to be used in digital photography. The RMI Digital Gray card avoids color casts regardless of lighting, and provides durability versus other traditional gray cards. This gray card has many advantages: Spectrally uniform - The card maintains its constant gray appearance in a wide variety of lighting conditions. Durable plastic material - Lightweight, strong and can withstand professional and amateur photographers. Waterproof - A gray card you will not be afraid to use in wet weather, or even underwater. Washable - It can be easily cleaned with soap and cold water to remove fingerprints and grime. Repairable - Small surface scratches can be repaired by the user with a random orbit sander. Note: The Digital Gray Card is designed for digital photographers only, as it is not an 18% gray. Reflectance is 30-37% (based on the light source) which will create inaccurate readings with film camera light meters.