This Artline Builders Marker Set contains six marker pens and is designed with builders in mind. The Builders Markers come in white and black, have a 2.3mm line width and write on various surfaces with UV light resistant ink, meaning there is no risk of it fading over time. The ink of the Exterior Marker is resistant to UV light and is waterproof, making it ideal for outdoor use. The permanent, waterproof ink of the General Purpose Marker is perfect for marking in the toughest environments and the Plumbers Marker is specially designed to write on wet and non-porous surfaces, drying instantly. The Concrete Marker has a heavy duty, long lasting nib and instant drying ink, making it ideal for marking coarse surfaces like brick and concrete.