The batsuit that Ben Affleck wears is based on Batman's suit in the comic book "The Dark Knight Returns," written by Frank Miller and published in 1986. The film itself is partly based on the graphic novel.
Ben Affleck asked Christian Bale for any advice he could give about playing Batman. Bale told him to "make sure you can piss in that suit." The two men met quite by accident in a costume shop. They were each buying a Batman costume for their kids.
Ben Affleck stated in a interview that he had asked if he could have the batsuit when filming was complete. The producers said yes, but that he would have to pay $100,000 in order to keep it. Affleck quickly changed his mind and asked if he could just take a picture with it instead.
In an interview with Jimmy Fallon, Ben Affleck said he was warned by Warner Bros. about the possible negative reaction to his casting, and was advised to remain off the Internet after the casting announcement. He also said to assuage his concerns, the studio showed him negative comments that fans had initially made to previous superhero castings. Affleck said in spite of the studio warnings, he still checked out an online message board. The first comment he read was, "Affleck as Batman? NOOOOOOOOO!!!!!!!!!!!" After seeing that, he immediately went offline.
Ben Affleck gained an additional 20 pounds of muscle and reached 8 percent body fat for his role as Bruce Wayne/Batman.
In this film, Batman wears a voice modulator in his suit to electronically alter his voice. After the casting of Ben Affleck in the role, this was an idea that had been suggested by his friend, director Kevin Smith, as he felt Affleck's natural speaking voice was too high-pitched for Batman.