The Osprey Aether 45 is a lightweight pack built to take abuse. This pack has no frame but uses a high-density foam back pad and laced compression cords to create a virtual frame. In our estimation, it comfortably carries up to 25 pounds (11.3 kg) for the average user. Our reviewer, who uses packs without hipbelts and admittedly has considerable tolerance for weight on his shoulders, found he could carry up to 35 pounds (15.9 kg) in the pack. The use of a roll-top with plastic reinforcements makes accessing gear easy. The Aether’s unique compression, in addition to shrinking the pack down for smaller loads, allows you to carry medium-sized items outside the pack. This is a solid and durable pack with reinforced seams, bar tacked webbing, abrasion resistant fabrics, and heavy-duty buckles. This durability comes at a price; at 2 pounds 4 ounces (1.02 kg) it is far from the lightest in its class. Further, its two side pockets, designed to be reached while wearing the pack, are difficult to reach and do not securely hold larger items like 1-liter water bottles.


  • Backpack Style – frameless, top loading, roll top
  • Fabric Description – 210 denier double ripstop used in main pack body and pockets. Heavier 420 denier “chainlink” fabric used on bottom, sides, and center of compression panel.
  • Sizes – S (14-18.5″), M (16-20.5″), L (20-22+”); size L tested
  • Volume – S = 2600 ci (43L), M = 2800 ci (46L), L = 3000 ci (49L)
  • Weight – 36.1 oz (1023 g) as measured, size L (Manufacturer claims weights of 28 oz for S, 30 oz for M, and 32 oz for L.)
  • Volume to Weight Ratio – 83 ci/oz (Based on 3000 ci, size L, and Backpacking Light measured weight of 36.1 oz)
  • Load Carrying Capacity – 25 pounds (BackpackingLight.com estimate)
  • Carry Load to Pack Weight Performance Ratio – 11.1 (based on 25 lbs and BPL measured weight of 36.1 oz)
  • MSRP – $99
  • Manufacturer’s Contact Information – Osprey Packs, 970-564-5900, www.ospreypacks.com


Numerical ratings follow on a scale of 1 to 5 (1 = poor, 5 = excellent).

Frame and Suspension – 3.5

The Aether 45 has a stiff, double foam backpanel but no stays. (While the addition of a foam sleeping pad would improve the “virtual frame,” our reviewer, who tolerates weight well on his shoulders, found that the backpanel was stiff enough to handle well-packed loads up to 25 to 30 pounds.) It has shoulder straps padded with high-density foam. The Aether 45 features a comfortable wicking backpanel that made hiking with a shirt off a joy. It wicked sweat away from the skin and toward the bottom of the panel. The hipbelt is also padded and features Osprey’s ErgoPull closure system. This system makes tightening the hipbelt easier and creates a V tensioning system on each side that improves the shape of the padded hipbelt. This pack has an adjustable sternum strap and shoulder lifter/stabilizers. All adjustments are easily made with the pack on. The waistbelt can adjust to fit approximately a 40 inch waist. The torso length is non-adjustable and the waistbelt is non-removable and non-replaceable.

Usable Features and Ease of Use – 3.0

The roll-top of the Aether 45 pack is stiffened by a sewn-in plastic rim, permitting the top to open like a clamshell to allow easy packing and access to items inside the pack. The Aether 45 does an excellent job of carrying a climbing rope. The climbing rope can be looped through the top of the roll-top and held in place with the side roll-top connections attached across the back of the pack. One ice axe/tool loop is included.

The unique laced rear compression cords adjusted quickly and easily with a single cord lock (it may occasionally require re-tightening). In addition, the laces offer the user an external place to stash a jacket, shovel, or small tent. A small fabric center panel hides a pocket for the extra lacing cord, which also worked well for stowing a small item such as sunglasses.

aether side pocket
It is difficult to access the side pockets while hiking.

The Aether 45 has triangular-shaped mesh side pockets that may or may not be accessible while hiking, depending on the user. One tester found that because the pockets are mid-way up the side panels of the pack, it was a struggle to remove anything but smaller items. Further, the triangular design allowed medium-sized items such as a 1-liter Platypus, a Nalgene bottle, or a large paperback book to fall out during technical sections or running (we didn’t ask him why he was running with a book). Don’t plan to carry long items such as trekking or tent poles in the side pockets. The side roll-top connections force the poles forward at an angle that puts the poles disagreeably near the wearer’s face. Our reviewer had better success weaving these items into the compression panel for a simple and secure solution.

The Aether 45 has an upper right side water bladder port with a convenient hose clip integrated into the sternum attachment. Despite having no internal or external hydration bladder pocket, our tester found that bladders remained stable in the pack when the compression panel was tightened and a few items were loaded in the pack to fill out the volume. While this pack has a sleeve between the backpanel and the pack body that could allow a hydration bladder to be inserted, the suspension design makes this very uncomfortable in practice and it is not recommended.

While it is possible to remove the padded back panel to use as a sit pad, our reviewer found this to be very difficult, especially with the pack full. The panel can, however, be removed and left at home to save a bit of weight.

Load Volume Flexibility (Compression) – 4.0

The Aether 45 has limited flexibility in handling larger volume loads. It does not have an extension collar and the compression panel is only able to handle one mid-size item (e.g., a small tent or a closed cell pad). It does a much better job with smaller loads; the compression panel is more effective at shrinking the space than the industry standard side panel compression straps. During one test in desert canyon country, the Aether 45 was loaded with only an insulated jacket and approximately 30 pounds of water; the pack carried this small, dense load very comfortably. Our tester found similar success with pack volume compression when using the pack as a daypack.

Field Performance

Pack Load Carrying – 3.5

The Aether 45 was quite comfortable with loads of 25 pounds (11kg). This was with the weight located in the center of the pack and the compression panel tensioned to create a “virtual frame” against the padded backpanel. As we increased the pack to 35 pounds (16 kg), the pack experienced torso length collapse that forced an increasing amount of weight onto the shoulders. Some users (those who can tolerate weight on their shoulders) will find the pack tolerable carrying up to 35 pounds. Even at these higher weights, the ErgoPull hipbelt kept loads evenly distributed on the hips, and the shoulder load lifters kept the pack riding close into the back. Because the Aether 45 rides close to the back, our testers felt agile and balanced when hiking or climbing.

When loads crept above 35 pounds (16 kg), the waistbelt started to slip and the pack became uncomfortable (and tolerable only for short stints even by a reviewer with some tolerance for weight on his shoulders).

While carrying small, dense loads such as when making water trips in the desert, the Aether 45 was able to consolidate the load effectively through tightening of its compression panel. This would also be true when using the pack with other low volume, high-density loads such as climbing or canyoneering equipment.

Osprey posted no suggested load carrying capacity; we suggest a maximum comfortable load carrying capacity of 25 pounds, though some will find it tolerable up to 35 pounds.

Durability – 5.0

The Aether 45 is constructed of durable materials that increase the pack’s weight but create a tough product. After a couple of weeks in Utah canyons in which the pack was lowered down pour offs, scraped through narrow slot canyons, and dropped off rocks, it shows very little wear. The only area that scuffing is visible is where the logo stitching on the back frayed a bit after sliding against narrow sandstone canyon walls. In addition, the plastic reinforcements for the roll-top opening wore small, insignificant holes in the fabric at their ends.

All seams in this pack are reinforced internally with webbing, and a tough Cordura is used at the bottom of the pack. Strap attachments are bar tacked for further durability. The high-density foam used in the waistbelt, shoulder straps, and back panel also showed no indication of compression fatigue. Buckles are heavy-duty Duratex models that didn’t crack, even when stepped on (which happened while standing on rock). This pack is built to last.

The material used on this pack, while durable, is not waterproof. Although the pack is somewhat water resistant, during both shower tests and a heavy rainstorm, items inside the pack got wet, as did the pack fabrics. Use of a pack cover is necessary with this Osprey pack.

Value – 3.5

At under $100, the Osprey Aether 45 is a good value. While a lightweight pack, it offers a comfortable suspension system, quality construction, durability for the long run, and usable options that many backpackers will find sufficient for their adventures. For its load carrying capacity and features it is on the heavy side for ultralight packs. Add some value points if you need a lightweight and durable pack.

Recommendations for Improvement

According to Osprey, the side pockets were designed with easy, pack-on access in mind. However, they are too high to allow easy access and too small to hold larger items well. Because these are the only exterior pockets, we would recommend redesigning the pockets to be deeper and rectangular to allow for carrying larger items more securely. Design changes that would allow the user to slip a hydration bladder between the backpanel and pack body would be both convenient and welcomed. This may require a more rigid backpanel or looser fabric behind the backpanel. Given the weight of the pack’s fabric, it would be nice if it were waterproof.