I had heard this urban legend that you can repair door dings and dents by rubbing dry ice over the dent and then heating it with a hair dryer or heat gun.
It seemed simple enough, so I decided to try it on the wife's urban assault vehicle which has its fair share of door dings. I went over to our neighborhood grocery store and got 2 pounds of dry ice for $3. Here is the what the test door looked like before the test.
Essentially the process is to take some dry ice (while wearing gloves, as it is very, very cold), and simply run the dry ice back and forth over the dent until the metal has cooled to the temperature of dry ice.
This shrinks the sheet metal, and pulls in the dent. Next blow hot air onto the dented area using a hair drier or a heat gun making sure that you don't heat the sheet metal to over 195 ~ 200 degrees as you can damage the paint by heating any more than that. This will expand the metal and further smooth the dent. After you have the sheet metal hot, then run the dry ice over the dent again until the metal is cooled to the temperature of the dry ice again. It takes about 3-6 times of this hot-cold-hot-cold routine to get complete results, but you will start to see the dent go away after the 1st cycle. Repeat this process until the dent is gone to your satisfaction.
Your end result should look like this:
This trick works even better with aluminum panels, does not scratch, discolor or harm the paint because the face of the dry ice on the sheet metal has a thin layer of Carbon Dioxide gas that is boiling off from the frozen dry ice.
I next tried this technique on another car of mine that has an aluminum body with a small ding on the left rear quarter panel, and it worked perfectly, and faster than a car with a steel body.
So $3 worth of dry ice and about 30 minutes saved me several hundred dollars for a paintless dent repair guy to do essentially the same job.
So never fear that your Golf or GTI will be marred with a door ding. Just fight back with a little Dry Ice and you are golden.