STILLMAN & BIRN Alpha Hard Cover Sketchbook - A6 Portrait (4 x 6" / 10.2 x 15.2 cm) - 150gsmOnly Stillman & Birn offers a sketchbook system that gives artists the choice of paper weight, shade, and surface type best suited to their specific techniques. With both internal and surface sizing, our papers have exceptional wet strength that supports the application of multiple washes. Similarly, just as the paper's sizing retards water absorption, pigment stays on the surface of the sheet. The result: remarkably glowing color! Stillman & Birn