Kapton (polyimide) tape is an insulation tape that is resistant to both heat and electricity.
Kapton tape is particularly useful as a surface material during 3D printing that involves a heated bed.
When a printed piece from a 3D printer is cooling it shrinks. If the piece cools unevenly then this shrinking will cause the piece to warp e.g. ends or corners curling upwards.
Using a heated bed as part of the printing process allows printed pieces to cool evenly and prevent warping.
When applied evenly to a glass surface, with no bubbles, Kapton tape makes the ideal surface for a heated bed.
Kapton tape is a good surface because it bonds easily to hot plastic and the cooled pieces can be easily peeled off the tape without damaging the part or the tape.