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Testing a Dry Bag at Home

What a home test can and cannot prove

Be clear about the boundary before you start. A home test answers one question well: is this particular bag, in its current condition, watertight enough for the trip I have planned? It does that by reproducing the three exposure types a bag actually meets, which are directed spray, brief shallow immersion and sustained contact with wet surfaces. It does not measure a rating to a standard, it does not predict ten years of service, and it says nothing about how the bag behaves at three metres.

That limitation is not a reason to skip it. Most dry bag failures in the field are not marginal engineering, they are a closure that was badly rolled, a grain of sand in the fold, a seam that has started to lift at a corner, or a valve left open. All four show up in a bath within ten minutes. The bag that quietly fails is the one nobody tested, and the most valuable result of a home test is often simply that it gets done at the start of the season.

Setting up a bench: bath, weights and a marker

You need very little. A bath or a large tub deep enough to submerge the bag to 30 cm, a stack of old towels, three or four paper towels, a 5 kg weight such as a filled water container, a non-permanent marker, a torch, and a notebook or phone camera for results. A shower head or a garden hose with a nozzle covers the spray test. If you have a kitchen scale, weigh the bag before and after each test: any gain above 2 g on a 20L bag is water getting in.

Two preparation steps matter more than the kit. Dry the outside of the bag completely and leave it at room temperature for at least two hours, because a cold bag condenses moisture on its inner surface and you will read that as a leak. Then mark the fold line with the marker before closing, so you can see afterwards whether the roll actually made three full turns rather than two and a twist.

Test one: the squeeze and listen check

This is the fastest test and it catches the majority of closure faults. Roll the top three times, clip the buckle, then press the bag firmly with both forearms and hold for ten seconds while you listen at the closure. A healthy bag gives a dull thud and holds pressure. A bag with a closure gap hisses, and the hiss will be directional, so move your ear around the roll to locate it. Repeat the squeeze at three different angles, because a fold that seals when pressed flat can open when pressed at the corner.

A slow hiss that dies away within two seconds is usually air escaping past the fold rather than a fault, particularly on a bag that was packed full of air. A continuous hiss while you hold steady pressure is a real leak. If the hiss comes from a hardware point rather than the roll, mark it and move straight to the bath test, because the immersion result will tell you whether it is a seal problem or simply air bleeding past a valve seating.

Test two: the ten-minute bath submersion

Fill the bath to a depth of 30 cm and check the water temperature is within about 5 °C of the room, which avoids pressure changes from thermal effects and avoids condensation on the inner wall. Pack the bag with something dry and absorbent: two bath towels work well because they show damp clearly and weigh enough to sink the bag partially. Close with three folds, put the bag in, lay the 5 kg weight across it so it sits fully under, and leave it for ten minutes.

Lift the bag out, dry the outside thoroughly with a towel, then open it and press a dry paper towel along the closure line, the base seam and every corner. Any grey mark on the towel is a fail. Weigh the towels you packed: a gain of more than 2 g on a 20L load, or more than 5 g on a 60L load, is water ingress even if you cannot see it. Record the result with the date, because the trend over seasons matters more than any single reading.

A marginal result deserves a second run rather than a verdict. Drain, dry the closure with a cloth, inspect the fold line for sand with a fingertip, re-roll with the bag filled only to the second fold line, and repeat. Most bags that fail the first run and pass the second were simply rolled badly or over-filled. A bag that fails twice at the same corner has a real fault and should go to repair rather than on a trip.

Test three: the shower spray pass

Immersion and spray are different stresses and a bag can pass one and fail the other. A directed jet at close range finds needle holes, imperfect welds around hardware and zip channels that a still bath will not reveal, because the jet is a localised pressure event rather than a uniform one. Hang the bag so it hangs freely, load it with 3 to 4 kg so the fabric is under slight tension, and spray each face for 60 seconds from about 50 cm.

Cover the closure, the base, all four corners and every hardware point, and rotate the bag so no area is shielded by the fold. Then pat it dry outside and repeat the paper-towel check. Pay particular attention around valves and clear windows, because these are bonded parts with a boundary to the film and they are where jet failures concentrate. If you have a pressure gauge on the line, 30 to 40 kPa at the nozzle is a realistic equivalent to heavy coastal spray.

Test four: the paper-towel closure test

This one isolates the closure from the shell, which is useful because the closure is the part that changes every time you pack. Lay a strip of paper towel along the full width of the mouth before you roll, close with three folds, clip the buckle, then leave the bag in the bath for ten minutes as before. Unroll and inspect the strip: a dry strip means the roll itself is sealing along its whole length.

A damp stripe tells you exactly where the roll failed, which is diagnostic. Damp at the ends but dry in the middle means the fold was not pulled tight enough at the corners, a very common fault on a wide mouth. Damp in the middle but dry at the ends means the bag was over-filled so the roll closed over gear instead of over air. A damp stripe across the whole width usually means grit in the fold or a deformed stiffener.

Test five: the float and trim check

The same bath gives you a buoyancy reading for free. Roll the bag closed with a normal amount of trapped air, place it in the water and see how much of it sits above the surface, then repeat with the air pressed out. A 20L bag with a healthy air pocket floats high and supports several kilograms of additional weight; the same bag compressed sinks to a slow neutral state. That difference is worth knowing before you decide whether a bag that goes overboard will be visible or lost.

Trim matters as much as float height. A bag with all its air at one end floats nose-up and, if it is lashed to a deck, pulls against its lashings in a way that loosens them over a day. Note the behaviour rather than trying to correct it: if you want a bag that floats predictably, distribute the air by packing loosely and evenly rather than leaving one large pocket. More on the physics is in our buoyancy science guide.

How deep and how long to go

Depth is where home testing must stay honest. Thirty centimetres of water produces about 30 mbar of pressure difference, which is enough to find any realistic closure fault and roughly a third of the pressure the bag would see at one metre. Going deeper in a bath is possible with weights, but it does not reproduce a controlled laboratory immersion and a pass at 60 cm still does not make the bag IPX7 rated. Test to 30 cm and treat anything deeper as a job for a lab.

Ten minutes is the right duration for the bath. Water moving through a capillary path in a fold is slow, and tests that run for only two minutes miss slow wicking entirely, which is exactly how a bag that seemed fine on a Saturday delivers a damp sleeping bag on Sunday. If you want more confidence, run two ten-minute sessions with a re-roll in between rather than one longer session.

Mistakes that produce false failures

Four errors account for most false alarms. Testing a bag that is colder than the room air, which produces condensation inside the shell. Over-filling so the roll closes over gear. Failing to dry the outside before opening, so water on the shell runs inside as you unroll. And reading a drop that fell in from your own hands as a leak. Each one is avoidable with thirty seconds of care, and each one has sent a perfectly good bag to the bin.

• Let the bag reach room temperature for two hours before any test.
• Fill only to the second fold line so three folds close over air.
• Dry the outside completely before you unroll, every time.
• Weigh the packed towels before and after rather than judging by feel.
• Re-run any fail once before you write the bag off.
• Keep hands and the rim dry when you open the bag to inspect it.

The reverse error is just as common: declaring a pass because nothing looked wet, when in fact 15 g of water went in and soaked into a towel. Weighing is what separates an opinion from a result. A kitchen scale with 1 g resolution costs very little and turns a vague impression into a number you can compare next season, which is the whole point of keeping a record.

Logging results over a season

A single test tells you about today; a log tells you about the bag. Record the date, the bag, the test, the mass gain and any mark location, and photograph the closure strip if it failed. Run the full set at the start of each season, after any repair, after any hard impact, and after the bag has been stored for more than three months. Three data points a year is enough to see a trend.

What you are looking for is drift rather than failure. A bag that gained 1 g in year one, 3 g in year two and 9 g in year three is telling you the film is losing flexibility or a weld is creeping, and it is telling you that well before it fails outright. That is the moment to demote the bag from expedition use to day use, which costs nothing, rather than discovering the problem mid-trip. Our seam integrity guide covers the degradation mechanisms behind the numbers.

When a home result should send you to a laboratory

Three situations are beyond the bath. If you need a documented rating for a retail listing, a tender or a warranty claim, a home test is evidence of nothing and you need a report from an accredited laboratory with the standard named. If you are comparing two candidate bags for a programme and the difference matters commercially, laboratory replicates remove the operator variable that dominates a home result. And if a bag passes at home but you still get water inside on the water, the fault is probably depth or dynamic pressure related.

Send the right samples when you do: three units from the same production batch, packed and closed by the same person, with a written instruction on the depth, duration and water type. Fresh and salt water give different results because surface tension differs, and saltwater testing is worth specifying for marine programmes; the detail is in our saltwater versus freshwater testing guide. Ask the laboratory to state the method it used, referencing ASTM practice where appropriate.

Programme buyers often ask whether a home protocol can stand in for incoming inspection, and the honest answer is that it complements rather than replaces it. Run the same five tests on three units pulled at random from a shipment and you get a practical check for about 35 minutes per batch, plus a record that shows whether a production run has drifted. Our own production team has built waterproof bags since 2014 in an SGS-verified 4,950 m2 facility, working to AQL 2.5 inspection with a 500-piece minimum and sampling in 6 to 10 working days; the route from drawing to freight is documented and the vocabulary behind the paperwork sits in our academy section.

Home results against IPX7 and hydrostatic claims

It helps to know what the labels mean when you read them against your own result. IPX7 means the item survived 30 minutes at one metre in a laboratory test, which is a far stricter condition than a 10-minute bath at 30 cm. IPX6 covers powerful jets and is what the shower test approximates. A hydrostatic head figure, expressed in millimetres of water column, describes fabric resistance to penetration under pressure and says nothing about the closure, which is why the two numbers on a spec sheet are not interchangeable.

So a home pass at 30 cm is a weaker claim than IPX7 and a home fail is still meaningful, because a bag that leaks at 30 cm will certainly leak at one metre. Use home testing as a screen and lab testing as evidence, and never put a rating on a hang tag on the strength of a bath. The grades themselves are defined by the IEC in IEC 60529, and our IPX rating guide explains what each one does and does not cover for dry bags.

A thirty-five minute routine, in order

1. Dry the bag and let it reach room temperature for two hours.
2. Mark the fold line, pack with dry towels and weigh them.
3. Roll three folds, clip, and run the squeeze and listen check.
4. Submerge at 30 cm under a 5 kg weight for ten minutes.
5. Dry the outside, open, and run the paper-towel check on closure, seams and corners.
6. Re-weigh the towels and record the mass gain.
7. Hang the bag and run a 60-second spray pass on each face.
8. Finish with the float and trim check, then log every result with the date.

Run in that order and each test feeds the next: the squeeze tells you what to look for in the bath, the bath tells you where to aim the spray, and the spray confirms whether the fault is localised. Total elapsed time is about 35 minutes including drying, and most of that is waiting for the ten-minute soak, so it is easy to run two or three bags in a single session.

If you own several bags, test them together once a season and rank them. The best becomes the expedition bag that carries the sleeping system, the middle one becomes the day bag, and the one that shows a slow drift becomes the bag that carries wet gear or gets retired. That ranking is worth more than any single pass or fail, and it costs one afternoon a year. Start with the procedure in our air inflation leak test if you want the quickest possible screen, then come back to the full set before a long trip.