Packing a backpack: load placement, access and staying upright

Packing is not tidying. It is placing mass so that the combined centre of mass of you and the pack stays close to the line your body already balances on, and so that the five things you need during the day can be reached without taking the pack off. Get those two right and a heavy pack walks lighter than a badly packed light one.

Where the mass goes, and the force it saves#

A pack applies two things to your body: a downward force equal to its weight, and a rotating force set by how far its mass sits from your spine. Only the second is under your control once the pack is packed.

Take a food bag and cook kit totalling 6 kg. Gravity pulls with 6 kg times 9.81 m/s squared, which is 58.9 newtons.

• Packed against the back panel, roughly 10 cm from the spine: 58.9 N times 0.10 m, which is 5.9 newton metres.
• Packed at the outside of the pack, roughly 25 cm from the spine: 58.9 N times 0.25 m, which is 14.7 newton metres.

Same 6 kg, same pack, and two and a half times the rotating force to resist for every step of the day. Your body cancels that torque by leaning forward, which shifts effort onto the lower back and shortens your stride. That is the whole reason "heavy things against your back" is repeated so often, and it is a lever arm, not folklore.

Vertical placement follows the same logic. Mass between the shoulder blades and the hips sits near the height of your own centre of mass, so the combined centre of mass moves very little from where your balance system expects it. Mass at the very bottom sits below and behind you, which pulls the pack away from your back and increases the lean needed to correct it.

High or low: matching the centre of mass to the terrain#

There is a genuine trade-off here, and the right answer changes with the ground.

High placement is more efficient because of posture: with the load near your own centre of mass you walk upright and the pack does not try to rotate you. Low placement is more stable because a lower combined centre of mass is harder to tip past the edge of your feet, and on rock or skis not tipping over beats a few percent of energy cost.

A practical compromise for most three season walking: dense items against the back panel, centred vertically on the region between the lower ribs and the top of the hip belt, with the heaviest single item highest in that zone.

The loading order, zone by zone#

Load from the bottom, and load in this order. Each zone is defined by what you need and when, not by what fits.

Two rules run across all six zones.

Symmetry. Balance the left and right halves as you go, particularly water. A full litre bottle in one side pocket and nothing in the other is 1 kg offset by roughly 20 cm, which is 2 newton metres of sideways torque. Your body corrects it by leaning, and a lean sustained for an hour becomes a sore shoulder, a sore hip and a blister on one foot.

Fill the voids. Air is the enemy of a stable load. Push socks into the pot, clothing into the gaps beside the food bag, and the sleeping bag loose rather than in a rigid compression drum. A packed load that cannot move does not shift on a descent. If you are consistently short of space, the problem is sizing rather than technique, and how many litres you need covers it.

Finish by tightening the compression straps. Their job is not to make the pack smaller, it is to stop the contents migrating downward and outward every time you step down. On a long descent, an uncompressed load creeps low and away from your back, and the moment arithmetic above turns against you without a single item having moved between zones.

The five things you must reach without stopping#

Taking a pack off costs two to four minutes each time, and the real cost is that people stop doing it. They walk on without the shell, or without drinking, because the pack is the obstacle. Design the outside of the pack around exactly five items:

1. Water. Side pocket you can reach, or a hose. If you cannot reach your own bottle, you will drink less.
2. A snack. Hip belt pocket. Food you never open does nothing.
3. The rain shell. Lid or top of the main compartment. The shell is only useful if it goes on before you are wet, and that decision is made in the first two minutes of rain.
4. Navigation. Map and compass in a hip belt or lid pocket. A phone in a zipped inner pocket is not navigation, it is a device you will not check often enough.
5. Sun and insect protection. Hip belt pocket. Same logic: friction determines use.

At the end of the day add a sixth, the headlamp, which should move to the lid before dusk rather than after it. The headlamp guide covers what to look for in one.

The test for this list is not importance but frequency: an item earns an outside pocket by being needed more than once between stops.

Liners, covers and keeping water out#

A rucksack is not waterproof. Seams are stitched, zips leak, and water resistant fabric loses that with abrasion. There are two answers.

A pack liner is a single waterproof bag inside the pack, holding everything that must stay dry. It weighs 30 to 90 g, has no exposed surface for wind to catch, works when the pack is on its side in a stream crossing, and cannot be removed by a gust. Its failure mode is a puncture, which is repairable with tape from a field repair kit.

A rain cover is a fitted shell over the outside. It weighs 60 to 150 g, keeps the pack fabric itself dry, and is quick to deploy. Its failure modes are structural: it lifts and flaps in wind, it leaves the back panel uncovered where water runs down between your back and the pack, and it fills with water in heavy rain if the drain is blocked.

The specification that matters for either is hydrostatic head, measured under ISO 811, the same test explained in waterproof ratings. For a liner, anything above roughly 1,500 mm is adequate, because it is never under sustained pressure. For sustained rain, our recommendation is a liner, with a cover as an optional extra if you want the pack itself to stay light rather than absorbing a kilogram of water.

Inside the liner, use a second layer for the things that must stay dry regardless: sleeping bag and sleep clothes in their own sealed bag. Wet insulation is the failure that turns a bad day into a serious one.

The two minute check before you walk#

Three failures account for most ruined days, and all three are visible before you leave the trailhead.

1. The hang test, for symmetry. Hold the loaded pack by the haul loop at arm's length and let it settle. It will hang with its centre of mass directly below the loop, so a pack that hangs tilted is loaded unevenly. Move a water bottle or a stuff sack across and hang it again. This takes fifteen seconds and prevents an hour of unexplained one-sided ache.

2. The reach test, for access. Put the pack on and fasten it. Without taking it off, retrieve your water, your snack, your map and your rain shell. If any of the four needs the pack removed, move it now. Doing this at the trailhead is the only time it is free.

3. The shake test, for shift. With the pack on, hop twice and twist at the waist. Nothing should move, thump or resettle. If the contents drop, tighten the compression straps and fill the voids. A load that shifts on a hop will shift on every step of a descent.

Then a last look: strap tails stowed so they cannot snag, liner closed and rolled, lid buckles fastened, nothing dangling below waist height. Under two minutes in total.

A weekend checklist to pack against#

Load from this list, working zone by zone in the order above. It is sized for a two night three season trip and assumes the fit decisions in backpack fit are settled.

Common mistakes#

Heavy items at the bottom. A widespread habit and the wrong way round for most walking. Mass at the base sits below and behind your own centre of mass, pulls the pack away from your back, and forces a forward lean all day.

The sleeping bag in a rigid compression drum. It saves volume and costs packing quality. A loosely stuffed bag fills the corners at the bottom of the pack and leaves nothing free to move.

Water on one side only. One litre is 1 kg. Split it, or move it as you drink.

Treating the rain cover as waterproofing. It does not cover the back panel, and it behaves badly in wind. Line the pack instead, and keep the cover for keeping the pack fabric itself dry.

Packing the shell where it needs unpacking. People walk on in rain rather than dig for a jacket, and then get cold. Put it in the lid.

Loose strap tails. They snag on branches, slap in wind, and pull compression loose. Stow or knot every one.

Packing to fill the pack. Space is not an instruction. If the kit ends 10 litres short of the capacity, compress it and carry the gap. The alternative is base weight creeping up for no reason.

Frequently asked questions#

Where should heavy items go in a backpack?#

Close to your spine and vertically between the shoulder blades and the top of the hip belt. Distance from the spine is what matters most: 6 kg packed 10 cm from the spine applies 5.9 newton metres of rotating force, and the same 6 kg at 25 cm applies 14.7. Height is a secondary choice that depends on terrain.

Should the centre of mass be high or low in a pack?#

High for smooth trail walking, because it keeps you upright and costs less energy. Lower for scrambling, skiing, boulder fields and stream crossings, where a lower combined centre of mass is harder to tip and balance matters more than efficiency. Most three season walking is best served by a middle position, level with the lower ribs.

Is a pack liner better than a rain cover?#

For keeping contents dry, yes. A liner weighs 30 to 90 g, presents nothing for wind to catch, works if the pack goes in a stream, and covers the back panel that a cover leaves exposed. A rain cover keeps the outer fabric from absorbing water, which is worth something in sustained rain, but it is a supplement rather than the primary defence.

What should I keep in my hip belt pockets?#

Items needed more than once between stops: a snack, sun protection, a compass, lip balm, a phone if you use it for photographs. The test is frequency, not importance. A first aid kit is important and belongs inside; a snack is trivial and belongs outside, because friction determines whether you actually use it.

How do I stop my backpack pulling me backwards?#

Move dense items against the back panel, fill the voids so nothing can migrate outward, and tighten the compression straps. Then check the fit: load lifters should pull the top of the pack in toward your shoulder blades, and the hip belt should sit on the iliac crest so the load runs down the skeleton rather than hanging off your shoulders.

Why does my pack feel heavier on descents?#

Because the load has usually moved. Every downward step lets the contents settle lower and further from your back, which lengthens the lever arm and increases the rotating force you resist, without any change in weight. Compression straps and a void-free pack prevent it. Retighten the hip belt at the top of a long descent.

Does packing symmetrically really matter?#

Yes, and it shows up within an hour. One litre of water in a single side pocket is 1 kg offset by roughly 20 cm, or about 2 newton metres of sideways torque. Your body corrects it by leaning, and a sustained lean produces one sore shoulder, one sore hip and often a blister on one foot. Balance left and right as you load.

How long should packing a backpack take?#

Loading a familiar kit takes ten to fifteen minutes once you pack the same zones in the same order every time. The part people skip is the two minute check at the end: hang the pack to test symmetry, reach for four items with the pack on, and hop twice to see whether anything shifts. That check catches the failures that cost hours later.