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Repairing a Punctured Dry Bag

Decide first whether the repair is worth doing

Not every hole deserves a patch, and knowing which ones to skip saves an afternoon. The three variables are location, size and age of the bag. Location matters most, because a patch on a flat panel sees almost no stress while a patch on a fold line is flexed every time the bag closes, and no adhesive survives that indefinitely. Damage within 15 mm of an existing weld is the hardest case of all, because the weld is thicker than the surrounding film and a patch cannot sit flat across it.

Size is the second filter. A pinhole or a clean slit up to about 20 mm can be patched with confidence. A tear from 20 to 40 mm can usually be repaired if it is on a flat panel and you reinforce from both sides. Beyond 40 mm, or any damage that has ragged edges radiating from a central point, the repair becomes a structural job and the bag should be downgraded to dry storage rather than trusted in the water.

Age of the bag is the quiet third factor. A bag older than about seven years has film that has lost plasticiser and UV stabiliser, and adhesive does not bond well to degraded polymer. You can recognise it by feel: new 0.5 mm TPU is supple and slightly rubbery, while aged film feels dry, stiff and faintly chalky. If the film feels like that, patch for storage use but do not trust the repair on the water.

Finding the hole: four methods that work

A puncture in a dark bag inside a dark tent is genuinely hard to find, and guessing wastes patches. Start with the simplest test: inflate the bag loosely, close the closure, and submerge it in a bath or a clean stream section by section. Bubbles mark the hole precisely, and a stream of small bubbles at one point means a pinhole while a sporadic large bubble means a slit that opens under pressure.

If there is no bath available, use the light test. Wait for dark, put a bright torch inside the closed bag and look at the panels from outside in a dark room. Even a 0.5 mm pinhole shows as a distinct point of light, and this method finds damage you would never feel. It is also the fastest way to check a bag you have just bought second-hand, and it takes about two minutes including setup.

The third method is tactile and works well for slits: run a dry thumb over the suspect panel with light pressure and feel for a raised lip. TPU tends to curl slightly at a cut edge, and that lip catches a fingernail. The fourth method is the paper-towel test, used when the leak is slow enough that bubbles do not show: line the bag with paper towel, close it, leave it in a bath for twenty minutes, and read the damp spot.

Reading the damage: four puncture types

The shape of the damage tells you how it happened and which repair will hold. A round pinhole is usually from a fishing hook, a thorn or a sharp buckle edge. A clean straight slit comes from a blade or a sharp metal edge. A star-shaped tear with radiating legs is an impact puncture from a pointed object such as a tent pole or a pump handle, and it is the one that needs the most care.

A crease crack is different again: it follows a fold line and is the result of repeated flexing in exactly the same place, which is why bags that are always folded identically eventually fail at the fold. These are the hardest repairs because the patch sits on a line that keeps moving. The mitigation is to extend the patch well beyond the crack, at least 25 mm on each side, so the flex happens in the patch material rather than at its edge.

One diagnostic step applies to every type: measure the remaining film thickness around the damage if you can. A 0.5 mm laminate thinned by abrasion to 0.2 mm or less is structurally finished even where it has not actually holed, and patching a hole in the middle of a thin area simply moves the failure to the patch edge. Thin areas feel noticeably floppier than the surrounding panel; trust your fingers on this one.

Adhesive patches on TPU: the default repair

A urethane adhesive with a matching TPU patch is the standard permanent repair, and it is what most people should use. The chemistry matters: TPU is a thermoplastic polyurethane, and a urethane adhesive bonds to it by slightly softening the surface and intermingling with the polymer chains. Contact cements and cyanoacrylate do not do this, which is why superglue on a dry bag peels off within days no matter how clean the surface was.

Preparation is ninety percent of the result. Cut a patch with rounded corners at least 25 mm larger than the damage in every direction; square corners lift first. Abrade the bag surface lightly with 400-grit paper to break the gloss, wipe with isopropyl alcohol, and let it flash off for two minutes. Roughen one face of the patch the same way. Apply a thin, even coat of adhesive to both surfaces and wait for it to go tacky before bringing them together.

Bonding is a one-shot operation, so position carefully. Lay the patch over the hole, then roll from the centre outward with a small roller or the back of a spoon to push adhesive and air toward the edges. Air trapped under a patch becomes a bubble that works its way out over weeks and leaves a channel for water. Apply firm pressure for two minutes, then clamp or weight the repair and leave it alone until full cure.

Heat welding a patch: the strongest home method

A heat-welded patch is genuinely fused to the bag rather than stuck to it, and on 0.4 to 0.5 mm TPU it is the strongest repair you can do at home. The principle is the same as the weld that made the bag: heat the polymer to its softening point, around 130 to 160 °C for most TPU films, press the two surfaces together, and let them cool as one piece. Too little heat gives no bond; too much heat melts through the film.

Use a domestic iron on a medium setting with the steam off, and put a sheet of baking paper or a silicone press cloth between the iron and the patch so nothing sticks. Work in short passes of three to four seconds, lifting the iron between passes and pressing the patch with a wooden block while it is hot. Watch the edge of the patch: when it goes from opaque to slightly glossy, the polymer has softened and the bond is forming.

The risk is overheating, and the symptom is immediate: the patch shrinks, the film around it puckers, and you have made the hole bigger. Practise on an offcut or on an old bag first, and start at a lower setting than you think you need because TPU softens faster than most people expect. If the film wrinkles or changes colour, stop, let it cool, and cut the damaged area out before starting again with a larger patch.

Tape repairs: what works and what does not

Tape is a field fix, not a permanent repair, but the right tape will get you through a trip. Clear repair tape designed for TPU and PVC inflatables works because its adhesive is formulated for the same polymer family. It will hold for days to weeks under water contact, though it will eventually lift at the edges. Apply it to a dry, alcohol-wiped surface, round the corners, and press hard from the centre outward.

Duct tape does not work on a dry bag. Its adhesive is rubber-based and designed for porous surfaces; on a smooth TPU film it holds for hours at best and leaves a residue that must be removed with alcohol before any real repair can be done. If duct tape is genuinely all you have, use it to hold a plastic bag or a piece of clothing over the hole as a mechanical barrier, then do a proper repair when you are home.

One useful trick for a field repair on a wet bag: dry the area, apply the tape, then warm it with the back of a spoon heated in hot water or with a lighter held well away from the film. Warmth softens the adhesive and roughly doubles the bond strength. Never let a flame touch the film directly. This buys you a day or two, which is usually exactly what you need to finish a trip.

Repairing welds and separated seams

A seam that has separated is a different problem from a puncture, because the failed area is a long line rather than a point and the load across it is continuous. Home repair of a welded seam is possible on a short section, up to about 60 mm, using the iron method with a patch that spans the full width of the failed area plus 25 mm of good film at each end. Longer separations need professional RF welding equipment.

The reason is pressure. A puncture repair is tested by immersion, which is a modest load. A seam carries the entire structural load of a filled bag, and the peel forces at the ends of a seam repair concentrate exactly where a home patch is weakest. This is the one case where we recommend sending the bag back rather than fixing it, and it is also the most common reason a repair fails after apparently succeeding.

If you do attempt a short seam repair, patch from both sides. A single-side patch on a seam will peel from the unbonded face within a few uses. Cut two identical patches, weld the inside one first while the bag is turned inside out and supported on a wooden block, let it cool fully, then turn the bag back and weld the outside patch over the top. Our seam tear guide shows the sequence with photographs.

PVC and coated fabrics: a different chemistry

A PVC-coated bag repairs differently from a TPU laminate. PVC needs a solvent-based cement that softens the coating and fuses it to the patch, and the solvent matters: tetrahydrofuran-based cements work, while the urethane adhesives used on TPU generally do not. Patches should be PVC of a similar weight and, ideally, from the same generation of material, because plasticiser migration between old and new PVC causes the patch to shrink and lift after a year.

Coated nylon without a film layer is the hardest case. There is no continuous barrier to bond to, only a cured coating on a woven substrate, and adhesion depends entirely on how much coating is left. If the coating has hydrolysed and gone tacky or powdery, no adhesive will hold and the bag is finished. If it is sound, a urethane patch will bond, but the repair will only ever be as strong as the coating underneath it.

Solvent safety deserves a line of its own. PVC cements and the solvents used to clean them are volatile and flammable, and they should be used outdoors or in a well-ventilated space, away from any ignition source. Dispose of used cloths and leftover solvent as hazardous waste rather than in household rubbish; the EPA publishes guidance on household hazardous waste disposal that applies to adhesives and solvents.

Cure times, temperature and clamping

Cure is where most home repairs quietly fail. A urethane adhesive develops handling strength in a few hours and full strength over one to three days, and the difference is chemical rather than cosmetic: the adhesive continues to cross-link long after it feels dry to the touch. A patch that goes into the water at four hours will usually survive but will not reach its rated strength, and that is the gap between a repair that lasts a season and one that lasts years.

Temperature is the variable you can control most easily. Adhesive cures by a chemical reaction that roughly halves in speed for every 10 °C drop, so a repair done in an unheated garage in February needs two to three days rather than one. If you are in a hurry, warm the area with a hairdryer on low before applying the patch and keep the repair above 18 °C for the first six hours.

Clamping is the second controllable variable and the one people skip. Even pressure across the whole patch area, about 2 kg over a 60 mm patch, is enough to keep the bond line thin and consistent. A stack of books on a flat board works well; a bulldog clip through a wooden block works even better because it localises the pressure. What does not work is a bulldog clip directly on the film, which point-loads and thins the adhesive at that spot.

Testing a repair before you trust it

Never assume a repair worked because it looks neat. A patch can look perfect and leak at one edge, and the only way to know is to test. The full sequence takes about twenty minutes including a drying interval, and it should be done before every trip where the bag matters, not just after the repair. Run it again at the start of each season on any bag with a patch.

1. Wait for full cure; do not test a patch that is still cross-linking.
2. Close the bag normally and inflate it until it is firm but not hard.
3. Submerge the patched area in a bath and hold it there for two minutes.
4. Watch for a stream of bubbles from the patch edge rather than the centre.
5. Dry the outside, then press firmly around the patch and listen for a hiss.
6. Leave the inflated bag for an hour and check that it has not gone soft.
7. Finally, pack the bag with its normal load and repeat the bath test.

The last step is the one people omit and the one that finds real failures. A patch tested on an empty bag sees no load; the same patch on a 10 kg load inside a squeezed hatch is under genuine stress and may open along one edge. If the bag fails the loaded test but passes the empty one, the repair is marginal: enlarge the patch by 10 mm on each side and repeat rather than hoping for the best.

How long a repair actually lasts

Expected life varies enormously by method, and the honest answer is that no field repair is as good as the original film. What you are buying with a good adhesive patch is several seasons of reliable use on a bag that would otherwise be scrap. What you are buying with tape is a week. Knowing which you have determines how you use the bag afterwards, and whether you keep a spare patch in the repair kit.

Two habits extend every one of those figures. First, keep the patch away from direct sun when the bag is stored, because UV attacks the adhesive bond line faster than it attacks the film. Second, avoid creasing through the patch: roll the bag at a different height for a few months after a repair so the fold line does not fall across the patched area. Both cost nothing and add seasons.

When to retire the bag instead

Repair has limits, and knowing them is part of good care. Retire a bag when the damage is on the closure fold line and cannot be patched outside it, when a weld has separated for more than 60 mm, when there are three or more separate repairs on one panel, or when the film has thinned across a broad area. Any of those means the bag will fail again soon, usually at the worst possible moment.

Retirement does not mean disposal. A bag that is no longer trustworthy in the water is still excellent dry storage: it keeps a sleeping bag compressed in a car boot, holds sandy beach kit away from everything else, or becomes a garden tool bag. Cut off the straps so nobody mistakes it for a working dry bag, and mark it clearly. This is the single most effective thing you can do to cut waste from water sports gear.

If you want to understand what caused the damage in the first place, our puncture resistance notes explain how films are rated, and the crease damage guide covers the folding habit that causes most long-term failures. Both are worth five minutes before you buy a replacement, because the failure usually repeats unless the habit changes.

Building a repair kit that fits in a pocket

A repair kit earns its place because punctures happen miles from anywhere. The whole thing weighs about 80 g and fits in a 2L roll-top. Assemble it once, check it at the start of each season, and replace anything that has gone hard or separated in the tube. Adhesive has a shelf life of roughly two years, so write the purchase date on the tube with a marker.

• Two pre-cut TPU patches with rounded corners, 60 mm and 100 mm across.
• A 15 ml tube of urethane adhesive, dated when you bought it.
• A 200 mm length of clear TPU repair tape for wet field fixes.
• A small piece of 400-grit abrasive paper for surface preparation.
• Three alcohol wipes in foil, which stay usable for years if sealed.
• A chinagraph pencil for marking the hole before you prepare it.
• A small wooden block or a spoon for rolling the patch down flat.

Add one thing for trips where the bag matters: a second small dry bag. A repair kit fixes the bag; a spare bag fixes the trip. Packing electronics and a phone in their own 2L roll-top inside the main bag costs almost nothing in weight and means a puncture becomes an inconvenience rather than an emergency. That is the same redundancy logic that paddlers use when they split kit across three bags rather than one.

Our production team has built waterproof bags since 2014 in an SGS-verified 4,950 m2 facility, and we repair and inspect returned bags as part of understanding how they fail in the field.Adhesion and peel performance is measured against recognised methods published by ASTM, which is the reference to quote if you need a repair to meet a documented standard.

For the kit itself, our patch kit guide lists exact patch sizes by bag volume, and the travel repair kit notes cover what to carry on a flight. Deciding whether a bag is worth saving is covered in when to retire a dry bag, and the short answer to the common question is in can a punctured dry bag be repaired. General care questions are answered on the FAQ page, and replacement builds are listed on the product line.