Originally developed for the U.S. Military, Rite in the Rain's soft cover books are made to survive. Made with only the most durable glues and materials to ensure your book won't fall apart in the field. The heavy-duty "perfect binding" holds strong through bad weather and years of abuse. Field-Flex covers easily conform to pockets or packs, yet spring back into shape - no worse for the wear. Rulers, conversion charts, and map scales printed on the cover prove handy in the field.