“Iron Lung” is rated R mainly for strong language, bloody imagery, and some gore, with an overall very intense horror tone.

Official rating reason

The MPAA rating description lists:

  • Language (frequent strong profanity, including repeated F-words).
  • Bloody images (the story involves an “ocean of blood” and disturbing visuals tied to that concept).
  • Some gore (there are a few graphic moments, especially toward the end, that go beyond what’s typical in PG‑13).

Because of this mix of harsh language plus disturbing, blood‑heavy imagery, it easily clears the bar for an R instead of PG‑13.

What it’s like in practice

People who have seen the movie say:

  • It’s not wall‑to‑wall graphic violence, but the blood concept and body‑horror elements are very unsettling.
  • There is at least one late‑film scene described as quite graphic and jaw‑dropping, which likely contributed to the rating.
  • Some viewers feel it actually earns the R more for foul language than constant gore, even though the setting is extremely bleak and creepy.

So the R rating is basically a combination of frequent strong swearing, a disturbing “ocean of blood” premise, and a few notably graphic shots, rather than nonstop torture‑style violence.

TL;DR: “Iron Lung” is rated R for strong profanity, disturbing bloody imagery (including an “ocean of blood”), and some graphic gore, especially in a few key scenes.

Information gathered from public forums or data available on the internet and portrayed here.