Some martial art styles that focus more on internal development and power may use this technique. Cotton palm differs from iron palm in that the latter tends to be more of an external force strike. When someone hits something with iron palm, they usually hit it pretty hard. As described in the other articles on this site, the external training features striking various hard materials in order to toughen the hand and penetration power. Of course, when properly done it also includes an internal component as well as dit da jow use.
Cotton palm training, on the other hand, usually involves hitting bags filled with cotton. The bags are usually not hit with much force, as the training is designed to focus qi. The strike is more internal in nature and relies on this rather than obviously generated external force, such as a physical slap.
It is worth mentioning that there is a bit of controversy surrounding cotton palm. On one side of the argument, you have people who insist that it is one of the highest levels of internal training. That an advanced practitioner can, with an apparent soft touch, cause significant damage to his opponent (or brick, or whatever he is hitting).
On the other side, you have people who think the entire thing is nonsense. If qi is even real, it surely can’t be used to attack your opponents. If you want to hit someone, hit them! You can’t lightly touch someone and shoot mystic qi into their body and cause them damage.
There is a third group of people, however, whose beliefs are in the middle. They believe that the fact that cotton palm looks like a light tap is because it’s just short power, and the force is applied over a small movement (quick acceleration). Of course, this has nothing to do with qi, and is instead entirely a matter of physics, just like the one inch punch.
There are likely some people out there who claim to have cotton palm, and who claim that it is mystic in nature, and probably have elaborate demonstrations to show you their power. As with anything of a mystic nature, the onus of proof is on the person claiming to have the power to prove that it is real (as opposed to being a charlatan trying to convince everyone that they have magic powers).
Be sure to read the 3 part series on this website about scams if you are inexperienced in dealing with mystic power scams.
Short power is one thing. In fact, short power is a useful skill to have. But if someone claims that they can shoot qi into a brick and break it with a soft touch, they should be able to demonstrate this ability in a way that cannot be explained away by physics, leverage, or body mechanics.