A regular plastic and rubber gas mask, used for filtering air for radioactive particles and poisonous substances. Widely used by rookies and veterans of all factions due to its universal functionality. Does not provide any physical protection.
Made out of rubberized fabric, the gas mask features two round visors and detachable filters. It's simplicity and low price make it an extremely popular choice among stalkers of all factions, who also tend to add faction-specific motifs to it.
The player begins Call of Pripyat with this occupying their head inventory – and it's encouraged the player either upgrade it or find a higher level replacement as soon as possible. It has by far the lowest durability of any armor item in the game – a single scan through an acid anomaly field, even avoiding the anomalies themselves, will likely take it to 50% condition or lower, and a single headshot can do roughly the same – if the player isn't killed.
Like its combat-oriented' counterpart, the steel helmet, the gas mask offers pitiful protection from only a small variety of the zone's dangers. Even fully upgraded, an out-of-the-box tactical helmet or curtain helmet will blow the Gas mask away in terms of overall protection.
A fully upgraded (and mint condition) Gas mask can be found near Joker's body if the player is feeling cheap.
Because of a typo in the upgrade script, or maybe because of an oversight, the Gas mask Psy Protection upgrade is ten times as effective as it was supposed to be; meaning that grabbing the Joker's Gas mask early can save the player a lot of trouble near the Scar Anomaly, any other psychic field or against Controllers.
In Shadow of Chernobyl, the Gas mask's lenses are transparent, making the wearer's eyes visible, but during Clear Sky and Call of Pripyat, odd-shaped black tints have obscured the lenses, likely due to aesthetic reasons.
Snorks wear a strange combination of GP-4 and GP-5 gas masks, which would indicate that it was the standard protective mask of the Ukrainian military until they decided to switch to the more modern PDE-1.
The gas masks commonly worn by stalkers is very similiar to the EO-19 PBF Soviet repirator, albeit with the filters exposed instead of concealed.
The Exoskeleton's gas mask more closely resembles the British Avon S-10 Respirator.
Loners characters (eg. Oleg Gusarov) and a cut Wind of Freedom suit Freedom faction member are characters in Shadow of Chernobyl that have a slightly different type of a gas mask. This is due to the fact that they use a slightly different character model, originally intended for the exoskeleton. The proper version was added in subsequent games.
Concept Art for S.T.A.L.K.E.R. 2 depicts characters wearing a wider variety of Soviet gas masks than in previous games, such as the PMG, PMG-2 (GP-6), and the GP-7. This is no real indication, however, of what would be achieved in the final game.
Stalkers are somehow capable of eating food and playing a harmonica, even while wearing a respirator, which has often been the target of humor by the STALKER community. In an interview (in Russian) with GSC regarding S.T.A.L.K.E.R. 2, an employee joked that "Well we had this little funny joke about that, their gas masks have a shredder that splits the food...", which can be heard at the 28:22 mark of the video.