User blog comment:YoshiRocker13/Fanfiction - Trustworthy/@comment-26939672-20161020224735/@comment-24200891-20161021060246

One underwear for obvious basic needs and another one for decoration of costume. Underwear outside is in old comic books because then drawers didn't know how to make superhero pants inapropriate. This became a joke. In modern comics and films Superman doesn't have red underwear outside.