Tombow Set of 12 Dual Brush felt tip pens in shades of gray felt tip pens with double tip, one tip is a nylon fibre tips giving accurate control when drawing, with flexible and versatile brushstrokes. On the other side of the pen, the fine tip is perfect for sketching, straight lines or handwriting. Water-based, with odourless ink, these pens can be mixed together or with other water-based pens or even watercolours.   The inks are acid-free and non-toxic.