The Marvy Le Pen Flex, with super-fine rubber brush tip is ideal for hand lettering artists while being durable enough for everyday use in notebooks and planners. The smooth, micro-fine plastic tip allows for precise writing, making it one of the best pens for bullet journaling. With its smooth, slim barrel that fits comfortably in the hand and colorful, quick-drying ink, Le Pen Flex is an instant favorite. The ink is acid-free and non-toxic. Colors with water-based ink.