This is coated with a very thin layer of glue. The problem is that if the glue were extremely good, it would prevent unwinding the roll. Stretching the tape activates the glue, so it will stick to the underlying surface and to the back side of the tape as you wrap and overlap. The stretched tape will try to pull back to its original length, and this tension increases its grip. In most machinery applications, a single layer of tape provides more than enough insulation for 12-volt electrical current.
Experienced technicians keep their electrical tape in the shirt pocket.
This also keeps it out of the direct summer sunlight, which can make the tape hot enough to fuse together into a useless mass. Most electrical tape is black, but it also comes in colors that make it extra useful for identifying which wire goes where in a complex electrical system. The insulation and adhesion are the same regardless of color. The other black tape, friction tape, is designed for strength, not insulation. This tape has a fabric layer that prevents it from stretching.