Please answer a question about the following article about Marvel Comics:

Lee and freelance artist and eventual co-plotter Jack Kirby's Fantastic Four originated in a Cold War culture that led their creators to revise the superhero conventions of previous eras to better reflect the psychological spirit of their age. Eschewing such comic-book tropes as secret identities and even costumes at first, having a monster as one of the heroes, and having its characters bicker and complain in what was later called a "superheroes in the real world" approach, the series represented a change that proved to be a great success.

What traditional superhero element did the Fantastic Four initially do without?
costumes