Pebeo Drawing Gum Marker Pen has an extra fine 0.7 mm nib for masking off detailed areas that you wish to remain white when painting with watercolours, inks or diluted gouache. The liquid frisket for watercolour & airbrush inside the marker is water soluble when wet and waterproof after drying. It can be used on paper, cardboard, Bristol board, acetate, wood and other surfaces.