The watercolor postcard books contain 16 cards made of the finest 250 gsm watercolor paper.  The paper is acid-free, FSC-certified and quite thick to make the cards suitable for mailing. They are a joy to color with a wide range of techniques, such as watercolor, ink, color pencil, crayon, etc. In order to get the best results, its recommended to use of high-quality coloring materials. Measures 4 x 6 in.