A regular black leather trench coat. Has no special purpose other than to keep the wearer warm at night or protect from a blind dog bite. Although the trench coat is not particularly comfortable, it is often used by Bandits in the Zone - either because it allows them to hide in the dark or simply due to its "cool" appearance. - In-game description
The in-game coat is basically a slightly worn, black leather trench coat with a hood and turtle-neck inner jacket. It's like a reincarnate of the leather jacket from the previous games, unable to protect the player from even a pistol round or anomalies as it lacks a bulletproof vest or anomalous protection equipment. It is, however, very light. The trenchcoat is usually worn by most Bandits, although some Loners wear it as well. The game also features a brown variant, unavailable to the player.
It only has a small upgrade tree. Its upgrade tree will outfit it with light steel plates and eventually a chain-mail vest to slightly increase its armor and a choice for a slight boost in anomalous protection. Although the latter requires the late-game calibration kit.
Since the trench coat is incapable of reliably protecting the player from anything, it should be ignored other than for humor or if one is looking for a tough survival challenge.