The ketone based ink of bic velleda whiteboard markers glides on smoothly and erases just as easily and is low odour to ensure comfort when writing extensively it features a strong acrylic tip that wont bend or retract into the barrel even with heavy use the bullet tip delivers a medium line of 14mm thickness thats perfect for any kind of whiteboard work this pack contains 4 markers in black blue red and green bullet tip whiteboard marker with slim barrel low odour erasable ink sturd