This permanent marker is non toxic and with Sureflow ink, if the cap is left off, it will continue to write for several days. This alcohol-based ink will permanently mark most surfaces, including wood, plastic, glass concrete and clean or printed metals. The body & cap of our Markers are moulded from high-density polyethylene, containing a non-toxic metal detectable additive. This compound can be detected by correctly calibrated in-line metal detection systems.