Custom Seahorse Pillowcase Standard 18x18 (one side) Pillow Cover PYC-1310 Custom Picture Pillow Cases 18" X 18" (one side). Made of 50% cotton, 50% polyester. The custom pillow case is without buttons,and has an opening on the side. With pre-shrunk fabric, this pillowcase is washable at 60. Having this soft custom pillowcase will add both comfort and style to your home.