Stillman & Birn Zeta softcover sketchbooks are flexible, yet strong with sewn bindings and rounded edges. White, extra-heavy weight 180lb paper has a smooth surface that is suitable for pen & ink, and dry media. The paper also has internal and surface sizing, allowing it to accept light washes, wet media, and watercolor as well. Paper is pH neutral, lignin and chloride free. Sketchbook measures 7.5 x 7.5 inches, with 26 sheets.