The flak jacket is an exceptionally useful piece of a equipment that allows Max to sustain more damage by increasing his maximum health. The flak jacket comes in multiple pieces spread across the various levels, typically hidden in secret alcoves, and don't have to be collected in any particular order; missed pieces can be collected in subsequent play throughs.
There are five pieces of the flak jacket in total. Collecting all of them is one of the game's achievements.
|Wormy meadows||The first available flak jacket piece is located in a small building directly north of the second swarm of worms in Wormy meadows. It is within the first secret area of the level alongside various pick-ups.|
|A bug's nest||The second available piece is located in a secret area behind a removable wall in the southeast corner of the winding tunnels. The wall can only be opened via a nearby panel that is almost completely invisible save for a faint green glow.|
|The machine runs on||This piece of the jacket is not hidden and is very easily visible, however, it is found during a section of the level where Max is being chased by a large surge of electricity, making the collection of this piece fairly risky. Fortunately, the game auto-saves just before the electrical surge comes to life.|
|The city is burning||The fourth flack jacket pieces is located in The city is burning, which is a fairly large level. After reaching the meeting point on the west end of the map, heading up in the direction of the abandoned factory and continuing east all the way to the eastern corner of the map will reveal a secret in an abandoned building which contains the piece.|
|Along the coast||The final piece of the flak jacket is located in an electrical power building just west of the lighthouse on the path of the optional quest to help Steve. As such, as long the player chooses to help Steve, this piece of the jacket is no trouble to obtain.|