Pure 100% cotton rag, premium grade, heavy-weight watercolor paper mounted to an extra heavy-weight .090" middle board. Uniform surface sizing and internal sizing provides maximum durability for wet on wet techniques, reworking and erasing. The convenience of an extra-thick, stable board eliminates soaking and stretching of watercolor paper. The surface is acid-free. Ideal for watercolor, acrylic and gouache paints as well as lightweight collage. Watercolor board is not recommended for oil paint unless primed with Gesso first. Board edges should be taped or waxed when heavy washes are used.