Hyperlite Mountain Gear Unbound 40 vs Bonfus Aerus 55L
Quick take: The Bonfus Aerus 55L costs $6 less; the Bonfus Aerus 55L carries more (55 vs 40 liters); the Hyperlite Mountain Gear Unbound 40 is lighter (1.71 vs 1.75 lbs).
Which one to buy
A sweaty back is the problem the Bonfus Aerus 55L sets out to solve, and the Unbound 40 does not. The Aerus suspends a tensioned mesh panel off a curved aluminum frame braced with carbon cross pieces, a trampoline layout normally found on much heavier packs, at 1.75 lb. The Unbound has the same clammy foam-on-back feel as every Hyperlite. The two weigh within 0.04 lb of each other and cost within $6.
The Aerus also holds more: 47 L inside plus 8 L outside, against the Unbound's 40. The Unbound rules out bear-canister country and long food carries, a hard limit, and it suits only a dialed sub-10-lb base weight with frequent resupply. Bonfus publishes a clear 33 lb rating, three torso sizes and two hipbelt lengths, which helps if your hips and torso do not match a standard pairing.
The Unbound's case is its pockets. Owners say its bottom stash pocket, for grabbing a layer or snacks without stopping, is the feature they cannot go back from, and its stretch front pocket dries a wet tent on the move. Warranty doesn't separate them much: Hyperlite guarantees the Unbound against manufacturing defects with no stated term, and Bonfus covers the Aerus for 2 years against defects. A trampoline back can also feel less stable than a contact back. For hot-weather thru-hikes and longer food carries the Aerus is the better-equipped pack, though in canister country you'll want to test-fit yours, since Bonfus makes no canister claim.
Hyperlite Mountain Gear Unbound 40
For dialed ultralighters with frequent resupply who value the bottom stash pocket and a stretch front pocket over volume and airflow.
Bonfus Aerus 55L
Better for hot-weather thru-hikers who want a ventilated back, more volume and a choice of hipbelt length without adding weight.
| Spec | Hyperlite Mountain Gear Unbound 40 | Bonfus Aerus 55L |
|---|---|---|
| Price | $395 | $389 |
| Rating | 4.8★ (4) | — |
| Type | Ultralight Pack | Ultralight Pack |
| Frame Type | Internal Frame | Internal Frame |
| Capacity | 40 L | 55 L |
| Weight | 1.71 lbs | 1.75 lbs |
| Max Load | Up to 40 lbs | 33 lbs (15 kg) |
| Torso Fit | 40L sized S/M/L/Tall, 55L XS-Tall: XS <15 in, S 15-17, M 17-19, L 19-21, Tall 21+ in | Sized S to 18 in / M to 19.5 in / L to 22 in; hipbelt short 29.5-39 in or M/L 33-43 in |
| Material | Dyneema Woven Composite 3.9, 100D Dyneema Gridstop, Dyneema Stretch Mesh | Ultra 200X with taped seams (UltraGrid option) |
| Back Panel | Two contoured removable stays | Tensioned mesh suspended off a curved 7075 aluminium frame with four carbon-fibre cross elements |
| Adjustable torso | No | No |
| Ventilated back | No | Yes |
| Raincover included | No | No |
| Hipbelt pockets | No | No |
| Removable lid | No | No |
| Hydration sleeve | Yes | No |
| Fits BV500 bear can | No | No |
| Warranty | Guaranteed against manufacturing defects, no term stated | Bonfus warranty: 2 years from receipt against material defects and workmanship failure; original owner, excludes normal wear and tear |
Pros & cons
Hyperlite Mountain Gear Unbound 40
- ✓The bottom stash pocket — grab a layer or snacks without stopping — is the feature owners say they can't go back from.
- ✓Waterproof Dyneema construction means no pack liner and no wet-gear anxiety.
- ✓At 1.71 lbs with two removable stays it competes with frameless packs while carrying meaningfully better.
- ✓The stretch front pocket (unlike the Southwest's solid one) swallows a soaked tent for on-the-move drying.
- ✓Build quality matches its flagship siblings.
- ✓The 40L discipline forces a genuinely light kit, which converts say improved their whole system.
- ✓Clean compression lets it double as a big daypack or peak-bagging bag.
- ✓The white-and-black aesthetic carries the same HMG cachet.
- ✗40 liters plus no bear-canister fit rules out canister country and long food carries — a hard constraint, not a preference.
- ✗$395 for less volume than a $229 Flash 55 makes the per-liter math painful.
- ✗HMG rates it to 40 lbs, but some owners find it carries best nearer 30 lbs; winter or water-heavy trips overwhelm it.
- ✗Same clammy foam-on-back feel as every HMG.
- ✗Fixed sizes, minimal try-on options, and a boxy fit — the standard HMG sizing gamble.
- ✗The stretch pocket wears faster than the Southwest's solid fabric in brush.
- ✗It assumes an already-dialed kit; beginners who buy the aesthetic first find it unforgiving.
Bonfus Aerus 55L
- ✓One of very few ultralight packs with a true suspended-mesh ventilated back.
- ✓795 g in the medium is light for a framed 55 L with that suspension.
- ✓Ultra 200X body with taped seams sheds water well.
- ✓Three torso sizes and two hipbelt lengths.
- ✓Bonfus publishes a clear 33 lb load rating.
- ✗$389 is among the highest prices for a 55 L ultralight pack.
- ✗Hipbelt pockets are a $27-each extra.
- ✗33 lb is a lower ceiling than some framed 55 L rivals that carry 35-40 lb.
- ✗A trampoline back pushes the load away from the spine, which can feel less stable than a contact back.
- ✗No stated hydration sleeve or bear-canister fit.
Hyperlite Mountain Gear Unbound 40 vs Bonfus Aerus 55L: common questions
Does the Aerus 55L's mesh back make it less stable than the Unbound 40?▾
It can. A trampoline back holds the load away from your spine, which some hikers find less stable than a contact back like the Unbound's. The trade is airflow, which the Unbound's clammy foam panel lacks.
Can either take a bear canister?▾
The Unbound can't: its 40 L volume and shape rule it out, so canister-country hikers need a bigger pack. Bonfus does not state canister fit for the Aerus, so check dimensions before relying on it.
Are hipbelt pockets included with both?▾
Neither. The redesigned Unbound 40 has none, and on the Aerus 55L they are a $27-each extra, which adds to its price if you want them.