These watercolor boards feature a 100% rag, heavy weight surface paper mounted to an extra heavy weight surface paper mounted to an extra heavy weight core. Uniform surface sizing and internal sizing provides maximum durability for wet on wet techniques, reworking and erasing. Best for paint like watercolor, acrylics, and gouache. Also good for light collage. Watercolor boards are extra thick to prevent warping. 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.