Metal Bullet PenPowder coated brass Convertible cap Pressurized, performs in temperatures from 30F to 250F and underwater Pressurized ink cartridge performs in temperatures from 30F to 250F, underwater (up to 35 ft), and at any angle. Compact when you need it to be but still offers the comfortable writing experience of a full size pen. Permanent ink writes through water, sweat, grease, and mud without clumping or smearing.