SOS field guides are made of white styrene plastic that can be written on underwater in pencel. The slates bendto help protect from breakage. Each slate has a hole includedto use witha lanyard (not supplied). Image may be of the front or the back. They are printed on both sides. The front has a history of the vessel and an above water image. The back has an underwater plan of the site and dive notes. Slates are about 6″x9″.