PEPIN Postcard Watercolour Books contain 20 cards, made of the finest acid-free watercolour paper. The 250 gsm paper is reasonably thick to make the cards suitable for mailing. Apart from watercolour, practically all other techniques can be used to apply color to the delicate designs in these books. PEPIN Postcard Watercolour Books match the quality of the finest professional watercolour pads. In order to get the best results, we recommend that you use high-quality colouring materials.