The Lightweight High Capacity Tank is a piece of equipment and an upgrade to the High Capacity O₂ Tank. It can be crafted at the Modification Station, after the player has retrieved its blueprint from a Data Box. The requirement for a Plasteel Ingot can be tricky early in the game, as Lithium is not particularly common in early areas.
Just like the High Capacity O₂ Tank, it boosts the player's oxygen supply by 90 units for a total of 135 units. However, it has a lower weight than the High Capacity O₂ Tank, allowing for no penalty to Swimming Speed.
The player must equip the Lightweight High Capacity Tank in the tank slot of the Paperdoll UI in order to benefit from it. While not equipped, it takes up six slots (2×3) in the inventory.
Note that when an O2 tank of any kind is built, it defaults to being empty: it must be equipped in an atmosphere in order to fill it. This is important if the player intends to carry multiple tanks for deep diving without a vehicle.