Pebeo Drawing Gum Marker Pen has an extra fine 0.7 mm nib - Blister Pack 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.