Preparation

• Before the dent can be removed, the surface must be cleaned. This is because things such as loose dirt, grime, loose paint and dust, if not removed, will become baked into the paintwork of the car and require considerable sanding and grinding to correct. The dent and surrounding metal should be washed and then rinsed thoroughly of any soap or cleaner residue before being towel-dried. With this done, one is ready to proceed.
  
  

Removing Dents

• A blow-dryer or house paint stripper is used to heat the dent evenly to the point where the metal would cause burns to the touch. Obviously one should not touch the dent, but simply feel the air over it. The warmth radiating from the metal should be palpable. The house paint stripper gets hot enough to potentially burn the paint of the car, so take care to stop before that happens. A can of air under pressure, such as the kinds that are used to clean electronics and keyboards, is shaken up and then sprayed across the surface of the dent. Because the can was shaken, it will spray out liquid CO2, which is very cold and will cause ice to form on the metal of the dent after a few seconds. The ice is left to melt in a few minutes. During that time, the dent will correct itself. Moisture from the CO2 evaporating is then wiped off where the dent was.
  
  

Why Does This Work?

• This process of heating and then chilling the metal removes the dent because of an interesting quirk of physics. Solid matter is not really solid. It's always composed of an incalculable number of component molecules with space in between them. These molecules vibrate depending on how much heat energy they possess. That's what makes matter go from one state to another: The molecules gain or lose so much heat energy that the change occurs. In this case, the change of matter does not occur, as not enough heat energy is used to cause it, but enough heat energy is used to cause the molecules of the dent to vibrate faster than normal. This causes the metal to expand slightly. The metal is then chilled with the CO2, making the molecules of the metal slow down very fast. Because they slow down so suddenly, the metal contracts, and it shrinks slightly as its molecules pack closer together. This contraction pulls the metal of the dent into line with the metal surrounding it, removing the dent.