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Are Dry Bags Airtight Enough for Electronics?

Waterproof and airtight are two different tests

A waterproof rating describes resistance to liquid water under a defined test. An airtight claim would describe resistance to gas flow across a pressure difference, and almost no soft bag is tested or rated for it. The physical reason is straightforward: a roll-top closure seals by pressing two film faces together, and that contact holds against a water film while remaining permeable to air once a pressure gradient builds. A bag can therefore pass a 30-minute immersion test and still hiss audibly when you squeeze it.

The distinction matters because electronics fail on moisture in any phase. Liquid water from a splash is one route. Water vapour that condenses onto a cold circuit board is a second. Salt-laden air that reaches a connector and never dries is a third. A bag that blocks the first can leave the other two completely untouched, which is why the useful question is not whether the bag is waterproof but which of the three routes you are actually defending against.

How a roll-top closure behaves under air pressure

Squeeze a closed dry bag and it hisses; that is the closure venting. The fold behaves as a relief path once internal pressure exceeds a small threshold, which is why a bag carried up a mountain or into an aircraft hold does not burst. It also means the bag cannot hold a vacuum or maintain a dry internal atmosphere the way a gasketed case with a clamp latch can, and it is the single most important fact for anyone packing a camera or a laptop.

The consequence is continuous exchange. Air, and the moisture in it, moves through the closure every time the bag is squeezed, warmed, cooled or taken higher. Over a day on the water that exchange can move several litres of humid air in and out. If the device inside is colder than the incoming air, the vapour condenses on it, which is the mechanism behind nearly every report of a phone that was in a dry bag and still ended up wet.

Condensation: the actual failure mode

Work the numbers. Air at 28 °C and 80% relative humidity holds about 21 g of water per cubic metre; the same air at 12 °C can hold only about 10 g. Seal 10 litres of the warm air and cool it overnight and roughly 0.1 ml of water comes out of suspension in a single air change. That sounds trivial, but the closure exchanges air continuously across a day of temperature swings, so the cumulative figure reaches 2 to 5 ml, which is easily enough to fog a lens element or bridge a charging connector.

The fix is not a better bag; it is less trapped air and something to absorb the moisture. Put electronics in a 2L pouch rather than loose inside a 20L, because the available vapour scales with the sealed volume, and add a 10 g silica sachet that will take up 2 to 3 g of water before it needs recharging. Dry the device before it goes in as well: a phone sealed with a damp screen brings its own moisture along for the trip.

Salt air and corrosion at the contacts

Salt does not need to arrive as liquid. In coastal air, chloride particles settle on exposed metal, and a connector exposed to salt-laden humidity begins to corrode at relative humidity above about 60%, well below the point where you would ever see liquid water. A charging port, a headphone socket or an unsealed camera contact is the usual casualty, and the resulting green deposit is frequently misdiagnosed as water ingress.

Mitigation is a barrier plus a rinse rather than a better bag. Keep devices in a secondary pouch so salt air has to cross two closures, rinse the outer bag with fresh water at the end of every day, and dry connectors with a lint-free cloth before charging. Where a device has been exposed, a fresh-water rinse of the connector followed by thorough drying works; rice does not remove chloride and can leave dust of its own.

Immersion ratings do not measure air sealing

IPX7 means the article survived 30 minutes at one metre without harmful ingress of liquid. It says nothing about gas tightness, and the standard that defines the grades, IEC 60529 published by the IEC, covers water tests only. A bag can pass IPX7 and still exchange air freely at the closure, so any claim of airtightness is a separate claim requiring its own test, normally a pressure decay or a vacuum hold.

If you genuinely need air tightness, look for a valve and a gasket rather than a roll-top. Bags fitted with a purge valve are designed to be inflated and to hold air long enough for a compression check, and some will hold a low pressure for several minutes. Hard cases with a silicone gasket and clamp latches hold far longer. Either way, ask which test was run and at what pressure, exactly as you would ask for the immersion standard.

Phone, camera and laptop: three risk profiles

A modern phone rated IP68 is already better sealed than any dry bag, so the bag's job is buoyancy, abrasion and loss prevention rather than water protection. A camera is the opposite case: a weather-sealed body tolerates splash, but a lens element fogs the moment warm humid air meets cold glass, and moisture at the sensor grows fungus over months. A laptop has no ingress rating at all and its keyboard deck funnels liquid straight to the board.

So the protection has to differ. Phone: a small pouch, a lanyard and a silica sachet. Camera: a padded insert inside a roll-top, a lens cloth, and a desiccant changed every second day on a humid trip. Laptop: a padded sleeve inside a dry bag, never a dry bag alone, because a few millilitres of condensate landing on a keyboard deck wicks in seconds. The laptop guide covers the sleeve detail.

The two-seal rule for electronics

Two independent seals separated by an air gap is the standard approach, and it works because each one has to fail separately. A phone in a 2L roll-top placed inside a 20L roll-top stays dry even if the outer closure is imperfectly rolled, and the inner pouch keeps the trapped air volume small enough that condensation is limited to a fraction of a millilitre. Put the silica sachet in the inner pouch, where it does the most good.

The rule extends to technique. Roll the inner pouch three times after pressing the air out, clip it, then do the same to the outer bag. Two bags rolled properly comfortably beat one bag rolled four times. Where weight and bulk allow, a small rigid case inside a roll-top is better still: the case supplies the air seal and the bag supplies the water barrier, the abrasion resistance and the floatation.

Desiccants, silica and dry cabinets

Silica gel is cheap insurance, but only if it is sized and recharged. A working rule is 10 g of silica for every 5 litres of sealed volume on a humid trip, recharged every 48 to 72 hours with 20 minutes in a 120 °C oven or a short low-power microwave cycle. Indicator beads that change colour remove the guesswork entirely; plain white gel gives no signal when it is saturated and quietly stops working.

At home, storage matters more than the bag. A device left in a closed dry bag in a damp garage is worse off than one stored open in a dry room, because the bag locks in whatever humidity was present when it was sealed. Use a dry cabinet or a sealed box with a rechargeable desiccant held at 40 to 50% relative humidity, and store the dry bag open with the mouth propped rather than rolled.

Battery safety inside a sealed bag

Lithium cells and sealed bags are a poor combination in two specific situations. The first is a damaged or swollen cell, which should never be sealed or carried in any bag at all. The second is heat: a cell charging or discharging inside a welded bag in direct sun can reach 55 to 60 °C, which accelerates degradation and, for a damaged cell, is the range where thermal runaway becomes a genuine risk.

The rules are simple. Never charge anything inside a closed dry bag. Keep power banks out of direct sun and off the bottom of a dark hull on a hot day. Carry spare cells with their terminals covered so they cannot short against keys, coins or a tripod plate. On aircraft, cells travel in the cabin and never in a sealed bag in the hold, where pressure and temperature both move.

Flying, altitude and pressure equalisation

Cabin pressure at cruise is typically held near the equivalent of 2,400 m, so a bag sealed at sea level carries roughly 20 kPa of additional internal pressure in flight. A roll-top vents, so nothing bursts, but the venting pushes humid cabin air in and out and can work the fold loose. A gasketed hard case holds that pressure and should be opened carefully after landing, using its pressure-release valve first.

The safe habit is to close soft bags loosely before flying and re-close them on arrival, and to point any gasketed case away from your face when opening it after a descent. For a device that has to stay dry in a hold, a welded bag plus a desiccant is still a reasonable answer, because the water barrier does not depend on the air seal and the bag will vent rather than fail.

Testing your setup before a trip

Two quick tests cover most of the risk. The first is the squeeze test: close the bag, squeeze firmly and listen. A continuous hiss from the closure is normal venting, while a hiss from a weld corner is a defect worth returning. The second is the cold test: put a dry tissue inside, seal the bag, leave it in a refrigerator for two hours, then check both the tissue and the inside of the film for moisture.

A third test is worth running once a season for anyone carrying a camera. Seal the bag with a fresh 10 g silica sachet and a humidity indicator card inside, leave it overnight, and read the card in the morning. If it has moved above 40%, the bag is exchanging more air than you assumed, and a smaller inner pouch is the fix rather than a bigger desiccant.

When a hard case beats a dry bag

Choose a hard case when the device is expensive enough that even 4 ml of condensation is unacceptable, when you are diving or working underwater, or when the trip involves repeated immersion rather than occasional splash. A gasketed case with clamp latches holds an air seal that no roll-top can match, and it carries the crush load that would push water through any soft closure at depth.

Choose a dry bag when weight, packability and floatation matter more, which covers most paddling, sailing and travel use. A 20L roll-top weighs 380 to 520 g against 1.4 to 2.2 kg for an equivalent case, floats when sealed with some air inside, and squashes into a hull or a pannier. The best answer for most people is both: a small case for the camera inside a roll-top for the water. Shore carry is the other place a soft bag wins, and our TPU waterproof backpack range uses the same welded construction with a harness instead of a single top closure.

A packing routine that keeps electronics dry

The routine is short enough to run every time and it addresses all three routes: liquid water, vapour and salt. Do it in the same order and it takes about two minutes, which is less time than it takes to dry out a phone. The point of the order is that the device is dry and sealed before it ever meets the outside of the bag.

1. Dry the device completely, including ports and lens mounts, with a lint-free cloth.
2. Place it in a 2L roll-top pouch with a fresh 10 g silica sachet and an indicator card.
3. Press the air out of the pouch, close with three rolls, and clip the buckle.
4. Put the sealed pouch inside a padded sleeve or a camera insert.
5. Place the sleeve in the outer roll-top, press out air, three rolls, moderate buckle tension.
6. Keep the bag out of direct sun and off hot decks; never charge inside a closed bag.
7. Rinse the outer bag with fresh water daily on coastal trips and dry the closure before rolling.
8. Open everything at camp, check the indicator card, and recharge the sachet every 48 to 72 hours.

Where electronics are the reason for the trip rather than an accessory to it, a rigid case with a gasket is the honest answer and a dry bag becomes the outer layer. Where they are incidental, the pouch-and-desiccant routine above is sufficient for paddling, sailing and travel in ordinary weather. Our own line has been produced since 2014 in an SGS-verified 4,950 m2 facility with 137 staff and 7 production lines, sampling in 6 to 10 working days and bulk in 35 to 50 days, FOB Xiamen.Water vapour transmission through films is measured by methods published by the ASTM. Further detail sits in the camera guide, the condensation guide and the IPX ratings guide.