Wool, a post-apocalyptic science fiction novel, is Hugh Howey’s first book. Originally self-published in 2011 as an e-book, Simon & Schuster later licensed it. The e-book features illustrations by Jimmy Broxton and Darwyn Cooke. Wool is the first book in Howey's Silo series, followed by Shift (2013) and Dust (2013).

Wool takes place in the world of the silo, a 144-floor underground community of humans, hundreds of years after an unknown event has caused the air above ground to become toxic. Expressing the forbidden desire to go out of the silo is punishable by cleaning. Cleaners wear suits designed by the IT department that allow them to stay alive long enough to clean the cameras that show the outside world to the residents inside. Eventually each cleaner succumbs to the toxic gases and dies. Most cleaners say they will not go through with the cleaning, but eventually all do, a source of mystery in the silo.

The novel opens with Holston, the sheriff of the silo, volunteering himself for cleaning. Three years earlier, his wife did the same after making a startling discovery in the silo’s servers. Holston, driven mad by grief and curiosity over his wife’s discovery, goes out to cleaning and discovers that the world is lush and alive, contrary to what he has been taught. He cleans the cameras out of pity for the people left behind in cramped silo. He soon realizes, however, that his helmet is showing him an altered version of reality and that the world really is toxic. He dies next to the body of his wife.

The mayor and deputy sheriff, Jahns and Marnes, go on a downward journey of several days to recruit a woman named Juliette for the role of sheriff. Juliette works in the “down deep” of Mechanical. She reluctantly accepts the role of sheriff in exchange for a power holiday that would give her enough time to make repairs on the silo’s generator. Jahns clashes with Bernard Holland, head of IT, over her appointment of Juliette as sheriff. Bernard, who is biased against mechanics and also furious over the power holiday, poisons Jahns canteen, assassinating her. Marnes, who was in love with Jahns, kills himself out of grief.

As sheriff, Juliette begins to investigate what drove Holston and his wife to cleaning, running afoul of Bernard, who is serving as interim mayor. She also meets Lukas, who works in IT, and starts a romance with him. Bernard banishes Juliette to Mechanical and soon after sentences her to cleaning. While she is in Mechanical, however, Juliette realizes that IT’s cleaning suits are designed to fail rather than keep cleaners alive. She devises a plan to secretly funnel higher quality supplies to IT for the next cleaning suit. Right before going out, Juliette also realizes that the visor of her helmet is showing her an illusion.

Juliette becomes the first cleaner in the silo’s history not to clean the cameras and to disappear out of sight of the cameras. Wearing a cleaning suit that actually protects her, she manages to walk far enough to come across another silo, exactly like her own except that its residents have all died after devolving into in-fighting. There she discovers first one survivor, a man she calls Solo, and later a group of wild children. She repairs a pump to dry the dead silo’s flooded levels, concocts a plan to dig laterally underneath and connect it with her home silo. She also discovers a way to communicate with people back home via radio.

Juliette’s failed cleaning causes turmoil back in the silo. The workers of Mechanical, riled both by Juliette’s arrest and disappearance and the revelation that the suits are designed to fail, plan an attack on IT. Bernard, meanwhile, prepares IT for the uprising and trains Lukas to be his replacement. Mechanical loses the battle against IT and is forced to retreat back to their levels, where they board themselves up behind steel walls. Lukas, as Bernard’s trainee, finds out that there are 50 silos in total and that the people who built them were also the ones who caused the extinction of most of the planet’s population. Unbeknownst to Bernard, Lukas is in communication with Bernard’s enemy, Juliette, in the other silo via the secret transmitters in the server room.

When Lukas starts to question Bernard’s murder of dissidents, Bernard sentences him to cleaning. Juliette finds out about the planned execution in time and builds a cleaning suit to go save Lukas. When she arrives back at her home silo, however, Lukas sacrifices himself to the cleansing fires in the airlock chamber rather than go outside. Looking at the body, she realizes that it was Bernard who died. Her replacement sheriff, having found out that Juliette was still alive, revolted against Bernard. Juliette is elected mayor of the silo after people submit an overwhelming number of write-in ballots. She decides that she will govern based on truth rather than deception.