Hyperlite Mountain Gear 3400 Southwest Review: Dyneema Light, Real-World Tough
The 3400 Southwest is the pack that convinced a lot of skeptical backpackers that Dyneema Composite Fabric was not just a niche experiment. At roughly 900 grams it carries a legitimate 55 liters, which puts it in a weight class that traditionally forces you to give up structure, pockets, or both. It is built for thru-hikers and fastpackers who have their kit dialed in and count every gram.
What we liked
- About 900 g for 55 L, genuinely competitive with packs that weigh twice as much
- Fully waterproof Dyneema Composite Fabric body, so a pack cover becomes optional in steady rain
- Removable aluminum stays let you run it framed for load transfer or frameless for shorter pushes
- External mesh pocket and daisy chains swallow wet gear, trekking poles, and a bear can without opening the roll-top
- Roll-top closure compresses the load as your food bag empties, which matters more than it sounds on a long resupply stretch
What to watch
- Fixed torso sizing (S/M/L) with no fine adjustment, so you need to measure before ordering
- No lid and no hipbelt pockets on the standard build, and the hipbelt itself is minimalist
- Dyneema is expensive and not as repairable as a cordura pack, so you are buying into a whole system
In depth
Dyneema Composite Fabric, explained without the hype
Dyneema Composite Fabric is a laminate: a grid of strong fibres bonded between thin film layers. The result is a material that is genuinely waterproof, very light for its strength, and low-stretch when tensioned. That combination is why it took over the ultralight shelter and pack world, and why a 55 litre pack can weigh under a kilogram without feeling flimsy in the hand.
The trade-off is abrasion behaviour. Dyneema resists tearing well but does not like being dragged across granite or scuffed against rock over and over. Where a heavy cordura pack will simply look worn, a Dyneema pack can develop pinholes and delamination at hard-wear corners after a few long seasons.
In practice, most owners protect the pack rather than the other way around: they set it down gently, avoid sliding it across rock, and keep a repair kit. Field repairs are straightforward with adhesive patches, and treating the pack as something to maintain rather than to abuse is part of owning one.
Sizing without adjustment: how to measure before you order
With fixed torso sizing, the measurement matters more than usual because there is no fine-tuning to fall back on. Measure from the bony bump at the base of your neck, the C7 vertebra, down to the top of your hip bones, following the curve of your spine. Have someone help, because doing it yourself skews the number.
Match that measurement to the size chart, then check the hipbelt sizing separately. A pack that sits correctly on the hips takes weight off the shoulders; a belt that is too small will ride up and put the load back on your trapezius within an hour.
If you fall between two sizes, think about what you carry. A shorter torso puts more weight on the belt and is generally more comfortable with heavy loads, while a slightly longer torso gives more room in the shoulders. For loads under about 10 kg, most people find either size workable.
Packing a roll-top 55 litres well
A single top-loading compartment rewards a system. The standard approach is a light sleeping bag or quilt at the bottom, then the heaviest items, food and water, pressed against your spine in the middle, then bulky light items like a shelter and puffy layer on top. Because there is no lid, everything you might want during the day needs a home outside the main bag, in the mesh pocket or on the daisy chains.
The roll-top is a feature, not a limitation. Every time you eat through a few days of food, you roll the top down further, which keeps the load compact and stops it shifting as the trip goes on. That progressive compression is one of the reasons long-distance hikers like this style of pack.
For bear canister trips, test the fit before you leave. A canister stands upright against the back panel in most 55 litre packs of this shape, but if you also carry a large shelter you may need to strap the canister outside, which changes how the pack carries and is worth practising on a short trip first.
Framed, frameless and knowing your limits
The removable aluminium stays let the pack cover two different jobs. With the stays in, the frame transfers load to the hipbelt and the pack is comfortable to roughly 14 kg, which is more than most ultralight hikers carry. Pull the stays out and you get a lighter, softer pack that hugs your back but relies on careful packing for any structure at all.
Frameless works when your total load is light, roughly under 9 kg, and when your kit is compact enough to form a stiff column inside the pack. A rolled foam pad or a folded shelter against the back panel does most of the structural work. Above that weight, most people find frameless carrying becomes tiring quickly and puts pressure on the shoulders.
The practical advice is to leave the stays in by default and pull them only for fast overnight trips or when you are deliberately shaving grams. Treat the option as a way to make one pack cover two trip types rather than as a permanent choice.
Waterproof does not mean worry-free
A waterproof pack body does not make your gear waterproof. Water still gets in through the roll-top if it is closed carelessly, straps wick moisture, and any pack left in a puddle will eventually let water through at seams and pin holes. The standard habit is a liner bag for the sleeping bag, because that is the item you cannot afford to get wet.
Roll the top at least three times before buckling, and check that the opening is folded squarely rather than bunched. If the closure is not clean, water can sit in the folds and work its way in during a long wet day.
Because the fabric does not breathe, condensation inside the pack is a real phenomenon on humid trips. Airing gear out at lunch, and packing the damp items on the outside, keeps the interior from turning into a terrarium over several days.
What to carry, what to skip, and when to look elsewhere
The gear that pairs best with a pack like this is the gear that does not need a lot of pockets: a rolled shelter, a quilt, a canister stove, a small filter and a single set of spare clothes. The gear that pairs badly is a camera kit with multiple lenses, or a winter load with a bulky synthetic bag, because neither compresses well into a single column.
If you routinely carry more than 15 kg, want a floating lid, or like a pack with organised pockets and a fully adjustable harness, a more traditional lightweight pack will serve you better and cost less. Ultralight gear only works as a system, and a pack is rarely the piece to start with.
The sensible sequence when moving in this direction is to upgrade the shelter and the sleep system first, carry less, and only then buy a pack sized for the load you actually have. Buying an ultralight pack before shedding the weight is how people end up uncomfortable and blaming the pack.
Questions we get asked
How do I measure my torso for a fixed-size pack?
Find the most prominent vertebra at the base of your neck, then the top of your hip bones at the iliac crest. Measure the distance between them along the curve of your spine with someone helping, and compare that number to the size chart rather than to your height.
Will a bear canister fit inside it?
Most standard bear canisters fit vertically against the back panel in a 55 litre pack of this shape. If you also carry a bulky shelter or a lot of food, you may need to strap it outside, which changes the carry and is worth testing before a long trip.
Can the pack be repaired?
Yes. Small tears and pinholes are usually fixed with adhesive patch kits made for laminated fabrics, and a few patches take up almost no weight. Larger structural damage near a seam is a job for a specialist repair service rather than a field fix.
Should I remove the frame stays?
Leave them in for anything above roughly 9 kg, or any trip with several days of food. Removing them makes sense for light, fast overnighters where the pack body is already full and rigid from the gear inside.