These cards are sized to fit into a #10 envelope and are perfect for greetings and correspondence. Slim Size matching envelopes are 9.5" x 4.125". Package includes 10 cards and 10 envelopes. Pre-scored Watercolor Cards. Made of 140 lb. cold-press watercolor paper, theyÃƒâ€ re ideal for wet media such as markers, acrylic, gouache and watercolor.