Which material handles the highest temperature?

Polyimide, by a wide margin among self-adhesive films. 3M’s Dot Matrix Printable Polyimide Label Material 7811 is rated for short-term exposure to 232 °C, with only slight browning after 7 minutes at 260 °C and no significant visual change after 30 seconds at 277 °C. Polyester such as 3M 7818 covers -40 °C to 149 °C long-term, enough for most machinery. Above the polyimide range, the answer is a metal plate.