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Ergonomics & Fit



We have a long term fit fixation: an obsession with designing and refining all the parts of the pack to best fit the widest range of body sizes and shapes.​ Each body-contact part of the pack needs to be precisely shaped to create a mirror image of this part of your body. Otherwise pressure points will be created leading to discomfort or pain. The spacing between the parts: hip belt, shoulder harness and backpanel must match the dimensions of your body. The body contact parts must also be positioned to softly transfer the load onto the bone structures of the body and avoid transmitting the load onto the muscles.​ Forty years of designing packs has allowed us to develop the simplest systems to precisely fit the widest range of body forms. We use multiple sizing and unique auto-moulding technologies.

The key features are:

  • All models except our smallest daypacks have adjustable back-length. for a precision fit. 
  • Larger models are available in 3 back-lengths, S, M & L, each size with adjustable backlength.
  • The backpanels on all our packs auto-mould to your back shape.
  • Shoulder harnesses auto-mould to the slope of your shoulders.
  • Shoulder harnesses come in 4 styles depending on pack volume, and each adjustable backlength style harness comes in 2 sizes.
  • Auto- mould hipbelts adjust in shape and length automatically as you tighten the hipbelt.
  • Pelvic-Form hip belts in 3 sizes. The overall shape is adjustable in curvature and length and the top of the hip belt auto-moulds over the top of your hips to your precise hip shape.
  • The joins between the back panel, shoulder harness and hip belt are smooth and continuous transitions.
  • The back panel, shoulder harness and hip belt are all highly breathable to minimise heat build up.
man fitting aarn pack


When checking other brands of pack, avoid models that concentrate the load by having separated padded areas and gaps in the backpanel or between harness parts. Thick padding in the backpanel does not necessarily increase comfort and moves the load farther away from your back. Especially avoid packs with a ventilation gap in the small of the back. Even if the pack frame is bent to the right shape, your back tends to round out into the gap towards the end of a long day due to fatigue, magnifying the spinal distress caused by the offset load.

Our pack frames bring the load as close to your back as possible while maintaining an air gap for back ventilation and preventing the contents of the pack touching your body. The suspended backpanel auto-moulds to your back shape in the same way that a trampoline will mould to your body shape as you land on it. The tension on the mesh backpanel can be adjusted for the optimum air gap between your back and the pack.


Our Back panels, shoulder harnesses and Hip belts are made from 3D mesh, with these outstanding characteristics:

    • Air permeability
    • Heat exchange
    • Shock absorption
    • Resiliency
    • Optimised Stretch
    • Low weight.

This allows all the body contact parts of the pack to auto-mould to the exact shapes of your shoulders, back and hips.



This is our sewn-in harness, used on our Ultralite daypacks and smallest overnight pack. Each shoulder strap incorporates large stretch pocket, large enough to take a 1L water bottle. Water is heavy and compact. It is the best item that can be carried in front to balance the load in your pack. If you are carrying only one water bottle, the other pocket can be used to carry a cell phone, camera or snacks. Everything in the shoulder strap pockets can be instantly accessed and reinserted without stopping or taking the pack off.


This is used on our larger day and overnight packs. It incorporates U Flow top stabilisers and bottom tensioners to allow free movement of the shoulders with pack stability. Backlength can be adjusted with the pack on via navy webs at the top and bottom of the backpanel to achieve the "feels right" fit. A double layer of foam is used over the collar bones to minimise possible bruising.


This is used on our mid to large volume packs. It incorporates Flow-Thru stabilisers and U Flow bottom tensioners to allow free movement of the shoulders with pack stability. Flow-thru stabilisers allow you to tighten the top stabilisers with distorting the shape of the shoulder straps passing over the top of your shoulders, which happens when the stabiliser straps are sewn onto the shoulder pads (the standard design). Backlength can be adjusted with the pack onvia navy webs at the top and bottom of the backpanel to achieve the "feels right" fit. A double layer of foam with roll over sides is used over the collar bones to minimise possible bruising.


This unique new harness is due to be released in January 2021. Initially it will be offered as an optional extra for those packs using the Bio-Fit Harness in order to receive valuable feedback on its performance. The key features of this harness are:

1. It disperses the load evenly over a much large area of the sternum to minimise fatigue.

2. It completely avoids the sensitive areas of the chest, making it especially suitable for women.

3. The interlinked U Flow chest and bottom tensioners allow full shoulder movement, maximum twisting between shoulders, and hips and maximum load stability. Because the chest and lower tensioner straps  are interlinked, they automatically adjust to equal tension no matter what your torso shape. 

4. Backlength can be adjusted with the pack onvia navy webs at the top and bottom of the backpanel to achieve the "feels right" fit.  

5.  A double layer of foam is used over the collar bones to minimise possible bruising.



These are used on our larger daypacks and light mid-volume packs. They use a twin web, dual adjust system to achieve a precise fit. The top webs go around your waist and wide lower webs go around the top of your hips. The tensioning webs connect to top and bottom adjustment buckles via one webbing loop, forming an easy to grab handle to tension the hipbelt. By adjusting the relative tightness of the top and bottom webs you can mould the hipbelt precisely to your hip shape, while automatically moulding the backpanel to your back shape!


These are used in our big packs. While the pelvis is a great load carrying structure, the hipbelt must be exceptional in design to take heavier weights without causing bruising over your hipbones or pressure on your hip sockets. Our large hipbelts are the result of many years of development and refinement. They incorporate our U Flow centre pivot and interlinked U Flow side connectors to allow unprecedented freedom of movement with load stability.

Sizing Our Pelvic-Form hipbelts come in 3 sizes to cover the whole range of pelvis sizes. Each has three parts, a central base and two ends. The 3 parts join together with velcro. You can micro-adjust the overall hipbelt curvature and the length by changing the velcro overlap.

Auto-Moulding Like the Auto-Form hipbelts, our Pelvic-Form hipbelts have separate top and bottom tensioning webs to the center buckle to distribute the load over the widest area. In addition, Pelvic-form hipbelts use a 2:1 pulley system to allow easy tightening with heavier loads. The tensioning webs connect to top and bottom adjustment buckles via one webbing loop, forming the same easy to grab handle to tension the hipbelt. By adjusting the relative tightness of the top and bottom webs you can mould the hipbelt ends precisely to your hip shape.


We don’t make separate mens' and womens' packs. We believe it is marketing hype to say one shape fits men and another fits women. This is because there is as much variation in the shape of backs, shoulders and hips within each sex as there is between sexes. (Chest shape is where men and women differ most ). The ideal solution is complete adjustability so you can achieve a mirror image fit to your unique size and shape, whether you are male or female.  To allow you to choosewhats best for your male or female chest shape, different types of adjustable Shoulder Harnesses are available for  the large packs . For On-Adjust and Bio-Fit shoulder harnesses, we have 2 sorts of chest straps: sternum straps (standard) and X Flow straps (optional) to cater for all chest shapes.


X-Flow chest straps eliminate the pressure and breathing restrictions of a conventional sternum strap, lightly disperse the load over the whole chest area for the greatest comfort and lock the pack close to the body for the greatest stability.

When Balance Pockets are used the sternum straps connect to the opposite side Balance Pocket to form the X flow system. These straps naturally lie clear of your chest. If not using Balance Pockets, you can clip on the optional accessory X-Flow straps


Why other packs increase back pain unnecessarily:

The traditional internal frame system, twin vertical stays, maintains the necessary vertical 'S' curve, but fails to prevent the backpanel rounding out horizontally into a convex shape when packed (Fig 1 & Drawing A ). Therefore the side profile of the pack is fat so that the load is positioned farther from your back. This increases the leverages on your shoulders and back, which results in a forward stoop and back strain.

An improvement in load distribution over this system is achieved by adding a plastic framesheet to the vertical stays to keep the backpanel flat horizontally ( Drawing B ), bringing the load closer to your back.

Suspended mesh backpanels have become popular in recent years. When poorly designed, these push the load far from your back (Fig 2 ), increasing forward lean. When well designed, (Figure 3, Drawing C ), they keep the load close to your back to minimise back strain as well as giving full back ventilation.


Aarn uses 3 different frame systems with our suspended backpanel to achieve good airflow with the slimmest side profile pack. Our top opening Daypacks use curved X-stays to give 3D shaping, while our panel opening Daypacks use a 3D shaped framesheet. Larger packs use an hourglass shaped perimeter frame and a horizontal strut to achieve the ideal 3D shaping with the lowest weight. In addition to creating the necessary the necessary vertical 'S' curve, all 3 systems create the concave backpanel shaping and the narrow pack side profile (C). Unfortunately it is not yet widely understood that the slimmest side profile is necessary to minimise the backwards pull on the shoulders and to minimise back strain.

This is why our packs appear bigger when viewed from behind but slim when viewed from the side. Of course you won’t find any large pockets or clip-on daypacks on the front of our packs farthest from your back, the worst position for load carrying comfort! Our Balance Pockets are in front of you to balance the load, and the larger models of Balance Pockets convert to daypacks when used alone.

Another fact that is not widely understood is that daypacks used for both walking and cycling need to be flexible in the vertical direction to fit the straight back of walking and rounded back of cycling. But at the same time the concave horizontal shaping needs to be maintained to keep the pack closely hugging your body. To achieve this, the lower backpanel of our daypack frames is flexible. The hipbelts are designed to nicely pull the lower backpanel on the pack into your lumber curve to give support to your lower back, no matter what your activity.


“The wide shoulder straps are comfortable, pliable, and not bulky. Some of the most comfortable I’ve ever worn.”
Ryan Jordan. Review, backpackinglight.com. Founder, Backpackinglight.com USA

"The shoulder straps were gently contouring and I experienced no neck pain, which has been a constant feature of my pack carrying life."
Paddy Pawson, Waipuna Community Trust, Christchurch

"This pack has many adjustments and while initially I needed to sit and work it out, the pack can be custom adjusted to fit any person’s frame size."
Paddy Pawson, Waipuna Community Trust, Christchurch