Internal Frame Packs vs External Frame Packs

You have it backwards. The point of an external, rigid frame is to allow the pack to put 100% of the weight on your hip bones, meaning your legs do most of the work. This method is far less fatiguing and much more efficient when walking on established, clear, maintained trails that don't have a tremendous amount of elevation changes. The problem with carrying all that weight on your hips is that when you lean to one side, the weight pivots from that point and the entire pack shifts. This makes them problematic for many challenging trails. Internal frame packs were first introduced for mountaineering, where control of the pack was far more important than weight transfer and covering long distances on trails. As such, the inflexible external frame was replaced with dual aluminum 'stays' that are basically flat bars that are bent to the users back. They flex under pressure and result in weight being carried in three areas - hips, lumbar region and shoulders. Because the pack is flexible, holds a lower profile and is weight bearing in three places - they are far more stable. In the mid 1990's vast improvements in internal frame designs all but rendered external packs obsolete, but they still have their place depending on your activity of choice. And I would argue that Zpacks are nothing but external frames in disguise, they are basically modern day versions of that design, but with carbon fiber frames which have both torsion flex and vertical flex, making them fairly stable.

The external framed packs I know didn't have a hip belt so I can't see how that puts the load on the hips. I can understand how they would if they did. I remember having a very sore back and shoulders... Does a Macpac Cascade have an internal frame or is it some sort of hybrid as I have seen mentioned elsewhere?

I can understand where the original idea came from. Early pack design put the weight on the shoulders. This was originally because most packs didn't have a waist strap and those that did only designed it to stabilise the pack not support it. Most external frame packs are of this vintage so cannot put the weight onto the hips. Early internal frame packs were not much better. New designs first seen in internal frame packs put the weight onto a hip belt which made loads more comfortable but really it was done to make the pack more robust and lighter. The benefit was exploited into the packs we have today where very little weight goes on the shoulders. The few companies still making external frame packs have also included these features so for a pack bought new today there is no real difference. Then there are the ultra light frameless packs which often have a moulded plastic board to mimic a frame and can give most of thee comfort but not with a full load of non ultralight gear

Obviously any backpack without a hipbelt cannot carry to the hips, and yes once upon a time they made those but for the past 30 years or so, I've never seen a reputable external frame without a hipbelt - it just doesn't make any sense. The Macpac Cascade is a traditional internal frame pack, very heavy (2800 grams empty)and very basic, I really don't see how packs like the Cascade have a market anymore but it shows the power of brand loyalty. Macpac packs are probably the weakest product they make, which is somewhat ironic considering it's what they are most associated with. If you want a really well made and durable pack, something that bridges the gap well is a ULA Catalyst or Circuit, and they weigh less than half of what something like a Cascade does. ULA keeps their packs light by keeping them simple, very basic, no frills designs, super durable and good suspensions. Unfortunately they ship direct to customer so you would have to buy one before you can try it - which kinda sucks.

if you go bush bashing off track, a macpac beats out the lightweight brands that get shredded in the NZ bush

I have seen an older version one of those packs and it was handling things quite well. The smooth finish doesnt snag on stuff (except bush lawyer) and this on had done a high mileage with lots of off track. The load ratings on those ula packs though is not that great. Ok if you have all modern gear ita adequate but 40 pound is something like 18 kg. If you are tramping in hot weather or where there is little opertunity to refill then you might be carrying 5kg or more of water. The Macpacs are as strong as anything else on the marketal though older tried and true fabrics tend to be heavier. Im going to be using my Torrlese for a good few years yet but its only 5 years old now.

I have a 23 year old Macpac which is indestructible. It has been everywhere and is still holding out well. I use my Osprey for less challenging tracks, but if I'm off piste and scrub bashing, out comes the Macpac. The Macpac also gets used for conservation work where I'm carrying tools, traps etc that might snag. They still have there place. If you're fit enough to head out and do some hard core missions, then the extra weight of a bombproof pack is no great problem.

...and on that note, if anyone has an old outer frame pack that they don't want, think about donating it to a conservation group or DOC. When you strip they old canvas off and just have the metal frame, they're great for strapping trap boxes to, birds being translocated etc. I was involved in a seabird project for several years where we would bungy cord birds in pet boxes to the external frames to move them over steep and difficult terrain.

Hunters love them to for much the same reason. External frame packs fetch good money on trademe