Actually, it's the other way around. It writes in black and when heat is applied it disappears. I printed the map off (canned campaign) and covered some important info with the pen.

Amazon link: Shomer-Tec Mossad Pen with Disappearing Ink https://www.amazon.com/dp/B00ABV7IOE/ref=cm_sw_r_cp_apa_i_hwVpEb0G0G7ZH