Storage
The Mercury 55 relies on a traditional backpack design and offers multiple access points that make packing, unpacking and accessing items very easy. A large lid, a zippered front pocket and two large hip belt pockets provided numerous storage and organizational options. The two side-stretch mesh pockets were deep enough to easily store and secure one-liter water bottles and allowed access on the fly. The zippers on the Mercury are seam taped, which greatly add to the performance and storage options of this pack.

Overall Comfort
The Black Diamond Mercury 55 was one of the most comfortable packs we’ve tested to date in this category. The rotating hip belt and shoulder straps perform well, adding to the comfort of the pack. The feature worked well along with the durable frame, and I found carrying loads from 40 to 45 pounds to be effortless.

Hip Belt
The Mercury incorporates a pivoting hip-belt that mimics your hip movements when walking. This system provided a greater range of motion and movement when compared to other packs that do not employ the pivoting hip-belt system. The hip belt also provides good padding and two large zippered storage pockets.

Backpanel/Shoulder Straps
The Mercury comes with a Swing Arm Shoulder Strap system, which incorporates straps that connect the bottoms of both shoulder straps, so pulling on one shortens the other, allowing you to move your arms more freely. Unlike the pivoting hip belt, I had a hard time identifying any added comfort or performance due to the Swing Arm shoulder strap system. The shoulder straps do come with a thick padding that makes them very comfortable when carrying loads up to 45 pounds. The back panel airflow was adequate, but not as good as in other packs I have used.

Stability
The Mercury 55 was stable and solid for carrying loads in the 30 to 45 pound range. The pack did not shift, or feel unstable in a variety of terrain and conditions. When loaded up to 50 pounds, I discovered that the Mercury did begin to float and move around on my back.

Durability
The Black Diamond Mercury 55 backpack proved tough and durable in a variety of weather and terrain. Black Diamond has seam-taped every zipper on this pack, which really adds to its performance and durability.