These iconic little blue sheets can be found at any popular drug or superstore and are a very convenient size.  They excel at their one job: removing oil from your face and neck.  As gross as it may sound, an entire industry has formed around variations of this product because of their convenience.  The form factor is incredibly convenient, as the package is about the size of a credit card so they can easily be stored in a pocket or purse.  Also, they could have been marketed specifically towards women, who I assume is their main target consumer, but because of their nondescript packaging and blue color, they are an ungendered product that makes them more comfortable to use in public for anyone.  They also work really well, and don’t require you to wipe your whole face as many moist wipes do, so if you wear makeup or cosmetics they won’t remove them.