Very cool picture,
SolarFett !
A lot of points already covered in this thread. An elaboration:
- All mandalorian armor was extremely personal, making the features of each one dependent on the demands of each individual as well as his budget
- This is not a question only regarding the helmet, but the whole armor working together with sealed pressure suits, neck seals etc.
- Theres mulitple levels in terms of what an armor / helmet could have been able to withstand:
- Germs / viruses / biological and chemical hazards in an atmosphere
- Underwater operations
- Vaccum
- So to speak: if its able to work underwater, its definatley also standing up to germs and viruses; If its able to withstand Vaccum, its also going to work underwater, etc.
- Obviously, there is more to this, as increasing depth underwater also adds pressure, which is a different issue then Vaccum and working for prolonged time in a contaminated atmosphere means air has to be filtered and purified, which brings with it a different set of equipment then "just" having that thing sealed with a small oxigen reserve to be able to survive an hour or so in vacuum or under water. But you get the idea

- None of this would have been a standard feature with mandalorian armor however, but an upgrade (as has been shown on the example of Jango by Irongladiator in his post, who didnt have a neckseal)
- It is safe to assume, though, that a fair percentage would have opted at least for air filters in their helmets, which would even be possible without neckseals
- There is evidence in the book "Star Wars legacy of the force 8 - Revelation", that there definately was Boba-Style mandalorian armor that was vacuum-sealed
However, in mandalorian armor upgrades like water and vacuum resistance would have been very expensive at the time of the movies and only very few Mandalorians would have had armor such equiped.
I know Kal Skiratas armor for example was not underwarter-capable.
It would have been definately possible, however to equip Mando armor in such a way, as seen in the book I mentioned.
Apart from that, there is definately personal armor in Star Wars, even ones closely linked to mandalorian armor, that had all of the features, namely, the Republic Commando armor. They had filters to avoid biohazards or chemicals in an atmosphere, could even survive in vacuum for a short period of time.
Ancient Mando armor, as was stated in this thread already, was more often equiped to handle vacuum, as can be seen here:
Now - how could that all have looked? I remember having seen a comic picture of a mandalorian withouth the helmet, where the neckseal was visible which ended in a metal plate that had the same form as the helmet base and sported what looked like "sealing and locking" equipment. Wasnt able to dig up the picture.
There is also a thread on tdh which shows how another solution could have looked like:
First apply 1" sticky back velcro to the skirt/gasket. hold the skirt so your looking at the raw side of it. Then fold the flap towards you so the clean side is showing. Make sure that it's taut then apply the velcro so it goes from corner to corner. Do that to all pieces except for the large...
www.thedentedhelmet.com
Hope that helps
-René