This is the Apeks WSX Redundant Air Cell 25lb OR 45lb OPTION Features: Apeks WSX Redundant Air Cell The WSX sidemount system now has a redundant option with the release of the new Apeks WSX redundant bladders. The bladders are cut to the same dimensions as the WSX-25/45 bladders and are made from the same ultra durable Armoguard material. They are designed to be mounted between the harness and bladder and have reversible inflators allowing the primary and backup inflators to be routed on opposite sides.