User blog comment:ReverseZoom101/2 Weird things you may or may not have noticed in The Flash/@comment-27700324-20161019153635

The burning clothes thing only works when you go a very fast speed. That is why Barry can go to the nearby battle agains't the Rival, and not lose all of his clothes. He goes to a really far away farm cause he was going too fast when he went through the dimensional barrier and Kara loses her work clothes.

Most of the time it is also for comedic reasons. Like that scene where Felicity was topless, or that scene where Kara also lost her clothes to burns, but she is Supergirl so she already had a top in the form of her costume.