The Pneumatic Chestplate stores a lot of air; considerably more than any armor piece (28000mL base storage compared to 12000mL for other pieces). In addition to that, the following useful upgrades are supported:

[prefix{l}]Security Upgrade[prefix{}]
With a Security Upgrade installed, the chestplate grants you protection from fire and lava, at a significant air cost: air is rapidly dumped from the chestplate to extinguish nearby flames and keep you cool.  It will even slowly solidify nearby lava.

[prefix{l}]Magnet Upgrade[prefix{}]
With one or more Magnet Upgrades installed, nearby items will be attracted to you for a very small air cost.  The base range is 5 blocks, but this can be increased up to 10 blocks by adding extra magnet upgrades.

The Magnet Upgrade respects Botania's Solegnolia flower, and will also not attempt to pull items from Immersive Engineering conveyor belts.

[prefix{l}]Charging Upgrade[prefix{}]
With one or more Charging Upgrades installed, the chestplate gains the ability to pressurize any other pneumatic item in your inventory, both worn and carried.  The chestplate will only charge items up to its own pressure level.  Adding extra Charging Upgrades (up to 6) increases the charging rate.

This works exceptionally well if many Volume Upgrades are also installed in the chestplate; until an Aerial Interface is available, this is the best way of keeping the armor running for extended periods.
