Side-by-side comparison based on expert reviews and community consensus.
Hyperlite Mountain Gear Southwest 55
Best UltralightOsprey Atmos AG LT 65
Best OverallPrice
$349-$399
$300-$320
Summary
Sub-2-pound Dyneema construction is fully waterproof, tear-resistant, and rated to carry 40 lbs — a combination no other ultralight pack matches. The go-to choice for serious thru-hikers on the PCT, AT, and beyond.
The suspended mesh back panel wraps onto the hip belt for unmatched comfort on multi-day trips. Lighter than the standard Atmos AG while keeping all the features that make Osprey the trail standard.
Pros
- Under 2 lbs (1 lb 13.7 oz) with Dyneema fabric that's fully waterproof and tear-resistant
- Rated to carry loads up to 40 lbs — far more than most ultralight packs (typically 30-35 lbs)
- Removable aluminum stays, foam back panel, and wide supportive hip belt for load transfer
- Available in 40L, 55L, and 70L capacities
- Suspended mesh back panel wraps onto hip belt for class-leading ventilation and comfort
- ~0.5 lb lighter than standard Atmos AG 65 at 4.2 lbs measured weight
- 65L capacity with lid, front mesh pocket, side water bottle pockets, and hip belt pockets
- External straps for attaching foam sleeping pads; side zipper for easy access
Cons
- Expensive at $399 — nearly twice the cost of the REI Flash 55
- Minimal organization: lidless design with streamlined storage may shock traditional backpackers
- Dyneema back panel offers poor ventilation — gets sweaty in hot climates
- At 4.2 lbs, heavier than ultralight options like the Granite Gear Blaze or Hyperlite Southwest
- Premium price tag around $320
- Less feature-rich than the standard Atmos AG 65 (fewer pockets, less adjustability)
Our take
If you're logging serious miles and want the lightest pack that won't fall apart, the Southwest 55 is the answer. It's expensive and minimal, but Dyneema's strength-to-weight ratio is in a class of its own.
If you only buy one backpacking pack, this is it. The Anti-Gravity suspension is genuinely different from everything else — testers describe it as a 'hug,' and after miles on trail, that's not hyperbole.
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