Green Slime Birthday Thank You CardsGreen Slime thank you cards feature words dripping with green slime and slime splats all over. With colors of black and green for a slimy way to send your thanks. Some features of our thank you cards: Professionally printed on 80# cardstock paper so you feel the quality. Teaches children how to send a meaningful handwritten note Easy to use because all you have to do is simply fill in and mail out 10 cards and 10 white envelopes included 4. 5" X 5.