The main purpose of the Boomer is to projectile vomit on Survivors. This covers their eyes in bile, making it difficult to see while at the same time attracting a horde of zombies to attack them. The Boomer is also the weakest Special Infected, having only 50 health and dying in 2-3 shots. However, upon death the Boomer explodes, shooting out bile everywhere and on nearby Survivors. This can be avoided by punching the Boomer before shooting him/her, which knocks the creature back to a safe distance.
The Boomer has short, black hair and appears in sweat pants, with a stain in them for an obvious reason, and navy sweater, stretched to breaking point by its vast gut, which makes it instantly recognizable from a distance. It makes belching, gurgling noises whilst in neutral pose, and groans when it sights a Survivor.
The Female Boomer (or "Boomette") is seen wearing a dark blue or black tank top drenched in bile, and shorts. Unlike the male Boomer, she doesn't have boils or growths. Instead, her skin folds forming flaps and perhaps highly Infected forms of tinea on the backs of her legs. The skin on her hands and wrists is black, and looks as if it could be necrosis. Her teeth seem to be horribly malformed either meaning she lacked proper dental hygiene before she became Infected, or that the virus or bile can damage the enamel and form cavities. She makes higher gurgling noises as compared to the male Boomer, and sounds more pig-like. In terms of gameplay, she functions exactly the same to the male Boomer.
The Boomer is the first in a line of Left 4 Dead Special Infected plushes being released by Valve, based upon the designs of Alexandria Neonakis who also created the Left 4 Dead Christmas card sets.