ABOUT:
Requested mod, that attaches Joel's gas mask to his face, so you can enjoy the entire game while wearing this not normally wearable headgear. 
The mod is also compatible with most of the current mods (that don't affect Joel's head .pak file.).

INSTALLATION:
1. Unpack the contents of the 'sp-common.psarc' file via "U4.PSARC.Tool", in: [YOUR GAME DIRECTORY]\build\pc\main
2. After doing so just rename the 'sp-common.psarc' (into OGsp-common.psarc for example.).
3. Put the modded/downloaded .pak files into the unpacked 'actor97' folder.
4. Enjoy the mod!
Alternatively, you can use "Fluffy Mod Manager", but I don't recommend it, as it currently causes inconceivable issues with the game. In case you ever want to revert, just rename the original .psarc file back to its original name 
('sp-common'), so the game can read only from the .psarc file again.

KNOWN ISSUES:
- Facial hair tends to clip a bit.
- The glass material still needs some tweaks, for it to reflect correctly.
- For unknown reasons currently, injecting the head mesh causes Joel not to load in the 'skins' & 'model viewer' menus.

If you'll encounter any other issues with the mod, then do let me know about them, so I can eventually look into it as soon as possible.

Special thanks to Speclizer for his 'TLOU Model Injector' & 'TLOU Texture Browser' and to Freako for his research.