Pigma Brush Pen Black Bold has a flexible nib for thin and thick brush lines. The extra durable, long-lasting and “memory” enhanced nib is made of BB, a tough porous polyethylene material Its durable brush nibs respond instantly to changes in pressure or direction, giving a silky smooth, accurate and consistent ink flow. The unique Sakura Pigma™ ink will not bleed through paper, is permanent, waterproof, fade resistant, quick drying and pH-neutral. Ideal for: Illustration, Journaling, Sketching, Rubber stamping, Comic Art. Available in other nib sizes and in a set."