No. 9 retractable blade is an excellent detail blade for making precise cuts through a range of lightweight materials. The fully retractable blade is thin enough to make the careful cuts you need but also sturdy enough not to snap under light pressure. Use with a large variety of medium and lightweight materials, including light cardboard, paper, film, cloth, plastic and more. Knife blades are crafted with sharpened carbon steel for a reliable cut and fit with most X-Acto retractable knife models.