Pilot FriXion

FriXion Clicker erasable gel pen An erasable gel pen that clicks, so there is no cap to lose. Rub out a mistake and the friction heats the ink past 140°F (60°C), at which point it turns invisible, which keeps practice problems, timelines and labeled diagrams clean enough to reuse. Tips come in 0.5, 0.7 and 1.0 mm; 0.7 is the middle ground for most handwriting. The usual FriXion caveats apply: heat can fade your notes, very cold temperatures can bring erased writing back, and Pilot does not recommend it for official documents. For flashcards you plan to keep all year, a permanent pen is the safer bet.