Electrostatic Discharge is the sudden flow of electricity between two electrically charged objects, usually after a build up of static electricity. On the largest scale, ESD is lightning and the accompanying clap of thunder. On a much smaller scale ESD might not even be seen but it can still cause tremendous damage to sensitive electrical equipment, as well as being capable of igniting flammable gasses and liquids.
ESD safe filaments have been designed for usage in applications that require protection from ESD, often in metering and sensing applications. ESD safe 3D printing filaments will have a surface resistivity given in Ohms. Surface resistivity is resistance to current across the surface of a material. The higher the Surface resistivity, the better the material is at insulating from ESD.
ABS based ESD safe filaments often have higher printing temperatures than their regular ABS counterparts.