"If you open your mind, you will see that all the elements are one. Four parts of the same whole. Even metal is just a part of earth that has been purified and refined."
Metalbending is a specialized sub-skill of earthbending that allows an earthbender to ferrokinetically bend processed metal in a similar fashion to bending regular earth. The technique was invented by Toph Beifong after Xin Fu and Master Yu captured and transported her in a metal cage, from which she escaped through the use of the skill.
During a lecture about chakras, Guru Pathik explained to Avatar Aang that metal is merely earth that has been purified and refined. Utilizing her unique ability to "see" using earthbending, Toph was able to perceive the trace amount of "unpurified" crude earth still present in the metal, target it, and use it to bend the purified metal itself.
No earthbenders were able to manipulate processed metal with their bending for thousands of years. This inability was demonstrated by many earthbender prisoners who were taken captive by the Fire Nation and forced to work on a prison rig made entirely out of metal, and also when King Bumi was suspended in a metal cage in the city of Omashu. Their incapacity to bend metal was also emphasized when Xin Fu and the Earth Rumble VI fighters captured Toph and Aang in cages fabricated with the material and suspended them in the air, a situation impossible to escape from through the use of conventional earthbending.
Toph was incarcerated in a metal cage during the spring of 100 AG by Xin Fu and her former teacher, Master Yu, when they lured her away from the rest of Team Avatar using a fake letter supposedly sent by her mother. While she was being transported back to Gaoling by her two captors, Toph desperately attempted to break the cage. However, Xin Fu commented that even if she was the best earthbender alive, it was still impossible to bend metal. At this point, Toph decided to test whether this was truly the case and, realizing that metal was only a form of processed earth, she began to meditate in her prison until she was able to feel the vibrations of the trace amounts of earth in the metal. By utilizing these remaining fragments, Toph metalbent for the first time, tearing a hole in her cage and allowing her escape while also imprisoning her captors inside the cage.
After the Hundred Year War, Toph established the Beifong Metalbending Academy and, by 170 AG, metalbending had become the primary form of earthbending used by Republic City's police force. The police use metal cables stored in cylindrical spool devices on their backs for various tasks, such as subduing criminals or for extra mobility around the city. The art also spread to earthbenders beyond the United Republic's borders, as some members of the Order of the White Lotus became proficient in the art. In addition, the city of Zaofu was constructed entirely by metalbending, an effort led by Suyin Beifong.
Toph's learning curve
Toph's metalbending seemed to be restricted to close-range manipulation. In almost all cases, she was standing close to or in direct contact with the metal she intended to bend. She had "scrunched" or otherwise deformed sheets of metal, but had never caused it to freely reshape itself the way she had with earth, and was not known to have ever bent metal at a distance. However, when making direct contact with a prison's metal door, she was able to blast it off its hinges with such force that it ricocheted four times around the corridor beyond before coming to a rest.
Toph later developed the ability to greatly increase the range of her metalbending, as she was able to knock several Fire Nation guards off the group's ship from several meters away, and developed the ability to "see" through metal just the same as she could with regular earth.
Other moments when Toph utilized metalbending include an instance in which she blasted another door off its hinges to free Hama's prisoners, opening a hole in the Fire Lord's secret underground bunker to grant Aang, Sokka, and herself passage, and trapping a Dai Li agent in a metal column.
Toph seemed to have furthered her ability to control metal by the time she, Sokka, and Suki set out to destroy Ozai's airship fleet, now controlling it more fluidly. She knocked off the hinges of the door to make a suit of armor in the same manner as the more traditional earth armor technique. She was able to manipulate the metal plating in the command bay of the airship from a short distance to pin her opponents to the walls. Toph was also able to metalbend the ship's floor upward to block a comet-charged fire blast just as a traditional earthbender would block attacks through earthbending using a rock barrier. She was additionally able to climb upside down across a pipe in the airship.
Toph later bent the rudder of an airship, causing it to spiral and collide with the other ships. When doing so, she took noticeably more time and concentration than if she had been required to do so with orthodox forms of earthbending.
A full year later, Toph was fully capable of bending metal she was not in contact with. For example, when a firebending teacher invaded her academy, she demonstrated her ability by effortlessly bending a metal weapon around his head that was a few feet away from her. She stated that as long as someone was close enough to see the metal, she could bend it. She demonstrated this by metalbending screws and bolts from a distance to unscrew the wheels of Fire Nation tanks. In her later life, she came to possess abilities such as being able to control cables from her armor, and being able to put on her armor, which appears to only be put on through metalbending.
Toph mentioned to Sokka while explaining how she found her students, that every time she was near each of them, her meteorite bracelet rumbled ever so slightly due to the intense emotional state those particular people were in. She realized that they were subconsciously metalbending the jewelry and thus figured that they had an aptitude for the art.
While teaching her first students the earthbending sub-skill, Toph forced them to remotely metalbend small coins rather than manipulate the metal via direct contact. Remote metalbending was favored over direct contact to break down the illusion of complete separation between bendable earth and purified metal at the beginning of the student's training.
Despite how widespread metalbending would become over the next 70 years, it is noted that only one out of a hundred earthbenders ever master the art, though master metalbender Suyin Beifong notes the only real limitation in learning the ability are the ones a person places on themselves.
Metalbending in Republic City
In contemporary forms of metalbending, the Metalbending Police Force can bend metals without direct contact. An example of this advancement was shown when Lin Beifong unlocked Korra's handcuffs from across the interrogation room with just a flick of her hand. In another instance, Lin was fighting Equalist chi blockers on the roof of the Pro-bending Arena. She knocked two chi blockers off the roof by metalbending parts of the support rods.
During the events of the Anti-bending Revolution, it was revealed that metalbending is ineffective against highly purified metal. An example of such a material is platinum, a metal that was used by Hiroshi Sato to create the mecha tanks to counter any effective resistance from the Metalbending Police Force. However, metalbenders can still use other bendable metals to restrain and attack the mecha tanks.
Other disadvantages of the sub-skill are its susceptibility to magnets, as evidenced when the aforementioned mecha tanks were equipped with these unorthodox weapons to subdue and electrocute the metal-clad police force.
Lastly, since the cables are also made of metal, they conduct electricity well. Therefore, if the opponent of a metalbender is equipped with electrified weapons, like the Lieutenant, he could send the shock through the cables, stunning the bender. 
- Beifong Metalbending Academy students
- Metalbending Police Force
- Metal Clan of Zaofu
- Toph Beifong (inventor)
- White Lotus sentry at Zaheer's prison
- Metalbending was alluded to by Aang when he offhandedly stated, "What I'd give to be a metalbender," as he tried to carve a notch in the hull of the Fire Nation drill with waterbending.
- Avatar Korra is the first Avatar to use metalbending.
- Metalbending is prohibited during pro-bending matches.
- Metalbending forms are based on Chu Gar with modern military techniques mixed in.
- The limitations of metalbending are portrayed differently in the Avatar comics. In The Bridge, Toph can clearly be seen using metalbending without direct contact in order to tie up the firebenders opposing her, whereas in the series, she does not manage to do this until the finale. In The Promise, Toph also tries to teach her students metalbending remotely first rather than with direct contact, though this may be because of inherent differences between developing the talent and teaching it to others.