Bonfus Aerus 55L

Ultralight backpacks are typically designed to be as simple and minimalist as possible, which often means the back panel sits directly against the user’s back—leading to excessive sweating. Bonfus accepted the challenge and solved it. The Aerus 55L features a curved aluminum frame that allows a breathable mesh panel to be tensioned between the pack and the wearer’s back. The result is a spacious, framed ultralight backpack that keeps your back cool and ventilated, even on long, hot days.

With a generous 55-liter capacity, the Aerus is perfectly suited for extended hikes. Thanks to the roll-top closure and side compression straps, it can also be compressed into a smaller, more compact form for shorter trips. While the recommended maximum load is 15 kg, users have successfully carried heavier loads without issues.

Features

The standout feature of the Aerus is of course its ventilated back system. A breathable mesh panel is tensioned between two 7075 aluminum frames, promoting back airflow. Stiffness of the mesh panel can be adjusted via its attachment points at the hip belt, which in turn affects the curvature of the aluminum frames. Four horizontal carbon fiber crossbars add torsional rigidity to the frame and prevent harder items in your pack from pressing against your back.

Both the mesh panel and hip belt are directly connected to the frame, ensuring efficient load transfer to the hips. For added comfort, the shoulder straps and hip belt are made with 11 mm thick EVA foam and lined with soft 3D mesh on the side facing the body. This same breathable mesh is also used in the neck area. A separate 8 mm lumbar pad adds structure to the hip belt and helps prevent sagging. The hip belt secures with wide 38 mm webbing straps.

The 55-liter volume is divided into 47 liters of internal space and 8 liters of external storage. In addition to the main compartment, the Aerus has two large side pockets accessible while wearing the pack, plus a spacious triangle-shaped front mesh pocket with an adjustable webbing under which gear like rolled-up foam pad can be secured. The roll-top main compartment is secured with a Y-shaped top strap that can also hold extra gear externally. Additional compression straps on the sides with quick-release buckles help cinch down the load or secure long items like trekking poles, tent poles, or fishing rods. Additional accessory pockets for the shoulder straps and hip belt are available separately to keep essentials within easy reach.

Materials

• Ultra 200X (130 gsm | 3.85 oz/sqy): Likely the most advanced pack fabric on the market. Woven from 200D UHMWPE fiber, it has three times the tear strength and seven times the abrasion resistance of DCF2.92. Backed with a 0.75 mil polyester film and X-ply reinforcement for waterproofing. Used for the main body of the pack.

• Ultra 400X (168 gsm | 4.95 oz/sqy): Woven from 400D UHMWPE fiber and backed with the same 0.75 mil polyester film and X-ply structure for waterproofing. Offers around twice the abrasion resistance of Ultra 200X. Used on the bottom panel for durability.

• UltraGrid (146 gsm | 4.3 oz/sqy): Woven from 210D recycled nylon yarn with a 5 mm 200D Ultra™ grid double ripstop structure for exceptional tear strength. Coated with a fluorocarbon-free DWR and a 1500 mm PU waterproof layer. Bluesign® approved. Used for the hip belt, shoulder straps, and side pockets.

• Taped Seams: All seams are taped for waterproofness and added durability. While the pack is effectively waterproof, a liner bag is recommended for river crossings or particularly harsh conditions to ensure contents stay completely dry.

Technical Specifications

• Volume: 55 liters (47 liters internal + 8 liters external pockets)

• Dimensions: Unrolled height: 87 cm | Average circumference: 96 cm

• Weight: 795 grams (size Medium)

• Recommended load: Up to 15 kg

Sizing

Torso Length (cm):

• Small: up to 45 cm

• Medium: 45–50 cm

• Large: 50–56 cm

Hip Girth:

• Short: 75–100 cm

• Medium & Large: 84–110 cm

Note on hip girth and pack sizing: please note that the measurements refer to hip girth at the height of the iliac crest (not waist girth, which tends to be smaller).

Assembly Instructions

Bonfus Aerus 55L is delivered with the aluminum stays detached. Assembly is quick and easy with the following instructions and Bonfus’ video guide.

1. Insert the Aluminum Bars: Starting from the channel opening at the base of the pack, insert the bars with the curvature facing the back panel.
2. Position the Carbon Crossbars: Ensure the top two carbon crossbars are positioned above the aluminum bars. To insert the aluminum bars into the top reinforcement pocket, use your fingers to squeeze the pocket entrance and enlarge the opening. Extra pressure may be needed for new packs.
3. Secure the Velcro Band: Thread the Velcro band on each side of the frame through the aluminum loop located on the back side of the hip belt, and pull it tightly to create tension in the back mesh panel and enhance the frame’s arch.
4. Attach the Mesh Panel Toggles: Use your hand and slightly press down on the mesh panel with your body weight, then insert the toggles into the grosgrain loops on both sides.
5. Ready to Use: Your Aerus backpack is now fully assembled and ready for use!