These markers are acrylic, lightfast, outdoor, water-resistant and have been designed with the mural artist in mind. With superior coverage, handling and pigment load, these paint markers works great on both interior and exterior murals. The bright colors are non-toxic and can be easily cleaned up with soap and water. A barrier coat and exterior grade varnish is highly recommended to protect outdoor murals. Always test on a small area before committing barrier coat or varnish to the entire project.