Writes through: the permanent ink writes through water, grease, and mud without clumping or smearing Pressurized cartridge: all-weather cartridge is pressurized, writes in temperatures from -30F to 250F, under water (up to 35 ft), and any angle Proprietary ink: The ink and delivery system used exclusively in Rite In The Rain refills will write without skipping in extremely wet conditions far better than other comparable all-weather pens