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Repairing a Dry Bag Seam Tear

Finding the tear: seam, weld edge or tape lift

Start by confirming where the water is actually entering, because the visible damage is often not the leak. Inflate the closed bag to around 5 kPa, which is little more than a firm squeeze, then brush soapy water along every seam and watch for bubbles, or submerge it in 30 cm of water if the body is small enough to handle. Work methodically around the whole perimeter rather than focusing on the corner you suspect.

Three failure types account for nearly every case. A split next to a weld runs in a single straight line just off the join, following the edge rather than through it. A crease pinhole appears as a cluster of tiny bubbles along a fold line. A tape lift shows a slightly raised film with a row of stitch holes visible underneath, usually starting at a corner.

Diagnosing why the seam opened in the first place

Every repair should start with a reason, otherwise you will be repeating it. The four common causes are ultraviolet embrittlement of the film around the join, flex fatigue from folding the same line several times a week, salt crystals abrading a fold, and sustained external pressure from a strap or hatch that drives the body against something rigid.

Each of those points to a different fix. Embrittlement means the body is ageing and the bag should be demoted from immersion duty. Flex fatigue means changing your packing so the fold line moves. Abrasion means better rinsing. External pressure means relocating the bag or padding whatever it rests against. Skip this step and the new patch will inherit exactly the load that destroyed the original.

One origin is frequently overlooked and belongs in a separate category: damage caused in production rather than ageing caused in service. An under-heated weld may look perfect while leaving only 60 percent of the intended film fused, and it will continue to accept load for the first several weeks before separating along a clean line. If a body tears within its first season at a location that has never been creased, abraded or compressed, treat it as a construction defect and raise it rather than simply patching over it.

Tools and materials for a workshop repair

The kit is modest and almost everything is already in a house or garage: sharp scissors dedicated to fabric, abrasive paper in 240 and 320 grit, isopropyl alcohol at 70 percent, lint-free cloths, a silicone sheet or a sheet of baking parchment, a rolling pin or rubber J-roller, flat boards and roughly 2 kg of weight, masking tape, a ruler and a marker.

Avoid two things in particular. Cyanoacrylate superglue cures rigid, and any flex in the film will crack it within days, leaving a harder edge that abrades the surrounding material. Solvent-cleaned surfaces also hate fingerprints, so keep a clean cloth within reach and do not touch the repair area after the final wipe.

Choosing a patch material that matches the film

The patch must belong to the same polymer family as the body. A TPU shell needs a TPU film patch or TPU-coated ripstop; a PVC shell needs a vinyl patch. Mixing them fails because surface energies differ and the adhesives involved are chemistry-specific, so the bond looks fine on day one and lifts cleanly two weeks later.

If you cannot tell which material you have, dab a little acetone on an inconspicuous inside edge. PVC goes tacky within ten to twenty seconds, while TPU stays matte far longer before it softens. Match thickness within about 0.1 mm as well, because a patch much thicker than the parent film creates a stiff island whose own edge becomes the next stress concentration.

Buying a little more than you need is worthwhile. A ready-made repair kit rarely matches the exact film in your bag, which is why building one from a known offcut pays off: keep a 200 by 300 mm piece of the correct repair film, a small tin of the matching cement, two grades of abrasive and a handful of lint-free cloths together in a sealed bag. Assembly advice is set out in the patch kit guide, and it takes less than an hour to put together from a single order.

Adhesives: which chemistry works on TPU and which on PVC

For TPU bodies, a solvent-based urethane contact cement or a purpose-made repair film is the dependable choice. Some of those films are heat-activated, fusing at roughly 120 to 160 °C under a silicone sheet. For PVC bodies, use a vinyl or THF-based cement that partially dissolves the surface so the two plies become one; contact cements formulated for TPU will not attack PVC adequately.

Whichever you choose, treat it as a chemical job rather than a sticky-tape job. Solvent-based cements release volatile organic compounds, so work outdoors or with real cross ventilation, keep away from ignition sources, and store offcuts sealed. The EPA publishes guidance on volatile organic compounds and indoor air quality worth following, and the CDC guidance on skin and eye exposure applies to solvent handling too.

Surface preparation that decides whether the patch holds

Preparation is where repairs succeed or fail. Rinse the area with fresh water, dry it completely, then abrade a zone slightly larger than the patch footprint with 240-grit paper, finishing with 320-grit. The goal is a uniform matte surface with no gloss left at all, particularly at the join edge where mould release or a surface treatment may still be present.

Wipe afterwards with isopropyl alcohol on a lint-free cloth and let it flash off fully. Work only above about 15 °C and below roughly 70 percent relative humidity, because both urethane cements and heat films dislike moisture held in the fabric. A bag used yesterday should be left open and dry for a full day before any patch goes near it.

Cutting and shaping the patch around a corner

Allow a minimum margin of 25 mm beyond the damage in every direction, and go to 30 mm where the tear sits near a strap anchor or a flexing fold. Radius every corner by at least 6 to 8 mm: square corners peel first, and a round patch will outlast a square one of the same area by a wide margin in any flexing position.

Where two seams meet, use either a cross-shaped piece or two overlapping patches with the second one rotated 90 degrees, never one shape folded over a corner. Along a curved edge, add fine relief cuts to about half the margin depth so the patch follows the profile without bunching, then seal across those cuts once everything else is seated.

Applying even pressure and getting the cure right

For contact cement, apply a thin even coat to both surfaces, wait the full open time until the film is tack-dry rather than wet, then bring the two together. Alignment is unforgiving once contact happens, so position a hinged piece of masking tape first. Roll from the centre outwards with firm pressure, working trapped air ahead of the roller rather than back into the bond.

Then leave it alone. Thirty to sixty minutes of clamped pressure between flat boards with roughly 2 kg of weight sets the bond; twenty-four hours delivers most of the strength, and forty-eight hours is better still. Resist the urge to flex or soak the area early, because the polymer network is still forming and premature loading permanently reduces final peel.

A pinhole behaves differently from a split and is worth handling separately. Because there is no open flapping edge, pinholes can often be sealed with a small round patch of 40 to 50 mm diameter rather than a large square, provided the cluster lies in a low-flex area. Several pinholes within about 20 mm of each other should be treated as one defect and covered with a single patch. The distinction between that job and a true cut is explained in the puncture repair guide.

Field repairs with tape, clamps and cable ties

Away from the workshop, aim for dry rather than for strong. Clean and dry the area as best you can, round the corners of a reinforced repair tape piece, and apply it with the bag inflated so the film is under gentle tension and has no slack to crease. Warm the tape with your hands first, especially below 10 °C, since cold adhesive barely wets out.

Clamping is the improvised part. A tent peg laid flat along the seam, two cable ties and a folded jacket will deliver enough even pressure for a few minutes, and a dry stuff sack packed tight over the area can hold it overnight. Expect temperate routine rather than immersion from a field job, and rebuild it properly within the week using the kit described in the travel repair kit guide.

Testing the repair before you trust it

Test in two stages. Within an hour of release from pressure, run a visual and thumbnail check around every edge of the patch looking for lift, bubbles or a glossy unbonded ring. At twenty-four hours, inflate the bag to about 5 kPa, hold it for ten minutes and check that the pressure drop stays below roughly 10 percent.

Then keep testing. Repeat the air check after the first outing, then monthly for the rest of the season, because repairs that are going to fail do so early. Retire the bag or rebuild the patch if any edge lift exceeds about 3 mm, since once air gets between patch and film, propagation is quick and irreversible.

What the repair will and will not restore

A well-executed patch gives back 60 to 80 percent of the original peel figure, sometimes more for heat-fused repair film applied to a clean flat area. What it does not restore is the flexibility of the surrounding body, the ultraviolet resistance of ageing film around it, or any of the material you removed during abrasion. Treat the repaired body as one grade below new.

That downgrade is manageable if you plan around it. Keep the repaired zone away from any fold line, avoid using the patch as a contact point against hard objects, and put electronics in a second sealed pouch from that point onwards. Reinforcing the area with additional internal padding costs a few litres and removes the conditions that caused the failure originally.

When a seam tear means the bag is finished

Some failures are not repairable in any useful sense. Multiple tears along the same seam indicate the whole join is failing rather than one point. Crazing across more than roughly a third of the body means the film has lost enough plasticiser or chain integrity that a new patch will simply tear free next to itself.

Two more signs are decisive: a weld line separating along more than 10 cm, and a surface that has gone tacky or sticky, which indicates hydrolysis rather than wear. At that point the economics favour replacement, and the retirement criteria in the end-of-life guide will help you judge it objectively. Anything past that stage can still serve as dry storage for non-critical items.

Keeping the repair from becoming a repeat job

Long-term success comes from removing the cause. Store bodies loosely rolled in shade, rotate the fold line every couple of weeks, pad every hard item so nothing concentrates load against one spot, and rinse after salt exposure so no crystals survive to abrade the film. Those four habits prevent most of the tears that reach a repair bench.

The same logic applies at the production stage: correct weld parameters, validated for each film and thickness, remove most seam failures before the bag ships. Our lines have run since 2014 in an SGS-verified 4,950 m² facility with 7 lines, 149 machines and 137 staff, sampling in 6 to 10 working days, bulk in 35 to 50 days and inspection to AQL 2.5 on a 500-piece minimum. We document the full process from sampling to bulk, and replacement bodies are listed alongside the current product range.

Finally, keep one honest habit: log the repair. Note the date, the method, the location and the outcome of your first test, and check it again before any trip where failure would matter. A single line in a notebook turns every future decision about that bag into an informed one rather than a guess made on a dark jetty. Repairing a body is almost always the better outcome on cost and on materials, and the arithmetic behind that choice is set out in the repair-versus-replace comparison; if anything is still unclear after reading this, the frequently asked questions page covers the cases we get asked about most.