Pro Art Painting Pad Watercolor Pad 12"x 16" Acid Free 140lb 15pc Block- Professional grade watercolor paper with a strong rough surface sized to withstand repeated washes and scrubbings. The specially treated neutral pH sheet enhances the brilliance of your watercolors. Blocks are sheets of paper which are glued together on all four sides and supported with a strong backing. You can paint on each sheet without having to stretch it or to worry about the paper buckling.