But that’s all right. The story’s familiar contrivances and clichés actually feel kind of cozy in “Cedar Rapids.” The film is burnished with the glow of sweetness not easily replicated by the Hollywood machine. That is no small feat, but the movie’s sly appeal is even more impressive when you consider how it also manages to be cheerfully profane.

Most of the credit belongs to Ed Helms. Having distinguished himself with TV’s “The Daily Show” and “The Office,” and the blockbuster comedy “The Hangover,” he proves he can carry the load of stardom. His portrayal of Tim Lippe, a mildmannered insurance agent in a sleepy Wisconsin town is a marvel of calibration, poking fun at the character’s naïveté while revealing his core nobility.

Tim’s world is rocked when he is sent to the aforementioned convention in Cedar Rapids, Iowa. It is a scary, but heady experience for a guy who evidently has seen little of the world. “The whole place smells like chlorine,” he gushes when he arrives at the hotel. “It’s like I’m in Barbados or something!” There, Tim must make a pitch for the office back home to win the coveted Two Diamonds Award, bestowed annually to the agency that best exhibits integrity and a sense of morality.

The setup is the stuff of Sitcom 101, to be sure, with the chief difference being that feature-debuting screenwriter Phil Johnston adds plenty of raunchy humor. No sooner does Tim arrive in Cedar Rapids before he is forced to room with Dean Ziegler (John C. Reilly, “Cyrus”), a loudmouth with a penchant for boozing and crass talk.

The mismatched pair is quickly joined by two other agents, straightlaced Ronald Wilkes (Isiah Whitlock Jr., TV’s “Rubicon”) and freewheeling Joan Ostrowski-Fox (Anne Heche, TV’s “Hung”).

These veteran conventioneers take Tim under their tutelage for a delayed coming-of-age marked by sex, drugs and drunken mischief. Our earnest hero lets his figurative hair down, learns the requisite life lessons and has his mettle tested. The path of the movie and Tim’s character are never in doubt.

What “Cedar Rapids” lacks in unpredictability, however, is made up for in charm. Directed by Miguel Arteta (“Youth in Revolt”), it reveals genuine affection for its flyovercountry populace. The filmmakers reject the mean-spiritedness seemingly obligatory in contemporary comedy, finding a sweet spot that elicits humor without belittlement.

And the cast is superb, as uniformly strong as any comedy in recent memory. Whitlock and Heche reveal ace comic timing, while the always-watchable Reilly ably shoulders the hard-R high jinks. Helms, however, brings it all together. His performance might not be the kind that earns awards, but it at least deserves the Two Diamonds.

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