High-Grade Filter

Type: Not a Hero
Chapter: NaH · Not a Hero · Salt Mines and Lab

Where

Mining Work Area, Cell: from your beheaded teammate's head, after Lucas's trap.

Effect

Fits onto the helmet by itself: you breathe without losing oxygen in mold-spore areas (most of the Storage Area). In Lucas's phase 2 your oxygen drops even with it.

Verdict

Mandatory: without it you cannot cross the Storage Area.