Arches Watercolor Blocks contain paper made with natural cotton fibers on a cylinder-mold machine. This artist-grade watercolor paper is great for watercolor, gouache, acrylic, and airbrushing. Arches is made with a natural gelatin sizing. These blocks contain 20 sheets of natural white, acid free, 100% cotton paper, and are glued on all 4 sides. This block is 18"X24" rough 140lb / 300g.