Bonded Seam Testing: What a Seam-Sealed Garment Must Pass

A bonded seam is signed off by tests a buyer can name: peel strength as bonded and again after washing, a hydrostatic head test where water is the requirement, and an appearance check against the sealed sample. All three run before bulk, on your fabric with your film, and the pass figure comes from the sample you approved. Bonded styles start at 200 pieces per style, per colour.

1. What each test proves, and what sets the pass line

A peel test measures the force it takes to separate two plies. Wash cycling shows what heat and water do to the adhesive over repeated laundering rather than in a single cycle. Appearance grading catches the faults that hold together and still look wrong: bubbling, tunnel wrinkling, edge curl, adhesive bleed. Hydrostatic head applies only where the garment has to keep water out, and where it does not, that test is not run and its absence is not a defect.

The pass line is set in your specification, or taken from the reading on the sealed sample. We report the value measured on your fabric, with the wash cycle it was measured at. A figure printed inside a standard is the industry’s, not a promise about your cloth.

2. What actually changes at the join

A sewn seam carries thread through two plies, leaves a stitch line and a row of needle holes, and turns the seam allowance inside. A bonded seam places a thermoplastic film between the plies and melts it into both faces under heat and pressure. No thread, no needle hole, no allowance: the join sits flat against the skin.

Seam sealing is a second line of defence rather than a third kind of join. Tape is hot-air applied over a seam, bonded or sewn, to close the pathway water would follow through a stitch line or a bond edge. A shell usually carries both.

Four processes carry almost all bonded work on our floor: hot-melt film on heat presses, ultrasonic welding where vibration melts the fibres together, laser cutting that seals an edge in the pass that cuts it, and seam tape. Ultrasonic welding needs synthetic content, because standard cotton will not weld. Our bonding room runs six bonding stations, four ultrasonic welders and one laser cutting machine, with settings logged per seam type.

3. Film and fabric are agreed as one specification

The adhesive film is not a consumable that works on everything. A film that holds a polyester interlock will not necessarily hold a cotton-rich knit or a brushed surface, and a silicone finish that feels expensive in the hand can stop adhesion altogether.

Three properties belong in the specification. Film chemistry: polyurethane films are softer and more elastic and suit knits, while polyester films give a firmer bond and are common on wovens. Film weight and melt index: a heavier film bonds more strongly and stiffens the hand, and on a knit over-specifying is the usual mistake, because the seam survives and the garment stops draping. Then the compatibility test itself — whether this film holds this fabric with the finish the mill actually applies.

If you supply the fabric, send the mill name, composition and finish with the enquiry. We run a bond trial before sampling: film selection, then a pull test and a wash cycle. You get the result before bulk is quoted, and on a blend we have not bonded before, it decides whether the style goes ahead at all.

4. Bonded seam testing: the methods, and what each one proves

The middle column is the method to name in your specification; the last is what the result is judged against, always your figure or your approved sample.

Bonded seam tests, the method to name, and what the result is judged against
Test	What it measures	Method to name	Judged against
Peel strength, as bonded	Force needed to separate the plies	Tensile pull on a bonded strip, ISO 11339 or ASTM D1876	The minimum in your specification, or the sealed sample reading
Peel strength after washing	Whether the adhesive survives laundering	The same pull test on washed specimens	The same figure, with the wash cycle stated
Hydrostatic head at the seam	Whether water passes through the join	Hydrostatic pressure test on the seam line	The figure your market requires, quoted at enquiry
Wash cycling	Bond behaviour over repeated laundering	Home wash cycles to ISO 6330 or AATCC 135	The cycle count agreed for your market
Appearance after washing	Delamination, bubbling, curl, adhesive bleed	Visual grading of the washed garment	The sealed sample

Two details separate a report from a number. The specimen comes from the bonded assembly rather than the fabric alone, because bonding changes the surface being tested. And it comes from the sealed sample or from bulk, not from a lab dip — a lab dip proves the film and the cloth met, not that the line can repeat the join.

Third-party testing can be arranged for peel and hydrostatic head on production samples, with laboratories in mainland China. Buyers who nominate their own inspector are welcome to do so, and we work to the standard that inspector applies; our own in-line checks and final inspection run to AQL 2.5 on top of the bond-specific checks.

5. From bond trial to bulk release: five gates

Five gates sit between a specification and a bonded bulk order, and two of them decide the outcome: the bond trial and the wash test.

The bond trial sets film weight, press temperature and dwell time on your actual fabric, then runs a pull test and a wash cycle. That result decides whether the style can be quoted, and it arrives before you commit to bulk. The first sample that follows confirms fit and construction only; nothing about the adhesive is settled at that stage.

The sealed sample is the second sample, built in bulk fabric with the approved film. It becomes the reference for the line and for inspection, and the press settings taken from it are logged per seam type. Move a bond line or resize a panel after sealing and the style goes back for a new trial, so raise changes while the sample is open.

Wash and peel on that sealed sample is the gate that either releases bulk or sends the style back. In the run itself, operators work to the logged settings and a drift stops the line rather than being noted and carried through; seams are then checked for skip, bubbles, misalignment and incomplete adhesion.

6. Where bonded seams fail, and what prevents each

Bonding replaces a forgiving process with an industrial one, and its failures are specific. Each is preventable at specification stage rather than at inspection.

Bonded seam failure modes, where they surface, and the control that prevents them
Failure	Where it shows up	What prevents it
Delamination along the bond edge	After repeated washing, at the edge of the join	Temperature, pressure and dwell qualified per fabric and seam type, then locked
Bubbles and adhesive bleed	On the press, or after the first home wash	Film weight and press window fixed on the sealed sample, not adjusted at the machine
Tunnel wrinkling and edge curl	After the first wash, along the bonded edge	Fabric heat-set or pre-shrunk before bonding, so cloth and film move together
Tape peeling at a hem	At the stress zone, before the tape fails	Tape width and stretch matched to the panel it sits on
Failure after a fabric lot change	Part-way through bulk	A bond trial on the actual bulk lot, because surface tension differs between dye lots

A bond that has already gone cannot be repaired. A sewn seam can be unpicked and re-sewn; a bonded seam cannot, and a mis-pressed panel is usually written off. That is a production fact rather than a sales point, and it is why the gates above are worth their days.

Bonding is not better in every direction. It is flat and carries no needle holes, and on a shell it can be made genuinely waterproof; it is less tolerant of high wash heat and dry-cleaning solvent, so the care label follows the tested film-and-fabric pair rather than bonding in general. Where a garment must survive hard wear and repair, a hybrid is often the honest answer: sewn where the seam is hidden, bonded where it shows.

7. Why bonded and seam-sealed styles start at 200 pieces

The minimum is 200 pieces per style, per colour, against 100 for the rest of the catalogue. Two colourways of one bonded polo are two minimums, and a different fit cut from the same fabric is a separate style with its own. Non-bonded styles on the same purchase order stay at 100.

The reason is the work before cutting: parameters dialled in on your fabric, trial panels and wash tests before bulk, fixtures made for your pattern, and fabric and film both procured to specification with the extra cutting loss a bonded marker carries. None of it shrinks with the order, and at 100 pieces it dominates the run. The construction runs on our seamless and bonded production line.

Sampling takes 3–7 working days and bulk 15–25 days after the sealed sample is approved; neither figure includes transport. Goods ship EXW, FOB Shenzhen or Yantian, or DDP. Payment is T/T with a deposit and the balance before shipment, or L/C at sight on a full container.

Frequently asked questions

What tests should a bonded seam pass before bulk?

Peel strength as bonded and after washing, wash cycling, appearance against the sealed sample, and hydrostatic head where the garment keeps water out. Colour fastness is tested on the bonded assembly rather than the fabric alone. The pass figures are your specification’s or the sealed sample’s readings.

Is seam sealing the same as bonding?

No. Bonding joins two plies with adhesive film under heat and pressure. Seam sealing applies tape over a seam, bonded or sewn, to close the pathway water would follow. A shell usually carries both, and which seams get tape is decided by your seam list rather than added afterwards.

Can a bonded seam be repaired if it fails?

A sewn seam can be unpicked and re-sewn. A bonded seam cannot, which is why a mis-pressed panel is usually written off and why parameters are fixed on a sealed sample before bulk begins. Where a garment must survive hard wear and repair, a hybrid build is often the right answer.

Will you bond fabric that I supply?

Yes. We buy from the supplier you nominate or work with fabric you send. Send the mill name, composition and finish, because the film is matched to the cloth and a silicone finish can stop adhesion. A bond trial on your fabric runs before sampling, so you know whether it bonds before committing.

Why is the minimum 200 pieces for a bonded style?

Because the work before cutting does not shrink with the order: parameters validated on your fabric, trial panels and wash tests before bulk, fixtures for your pattern, and fabric and film both procured to specification with extra cutting loss. The rest of the catalogue starts at 100 pieces per style, per colour.

Next step

Send the reference sample or tech pack, the fabric with its composition and weight, the seams you want bonded rather than sewn, and the quantity per colour with the size range. The reply covers the route we would use at each seam, the tests we would run on your fabric, and a sampling plan. Buyers still deciding between routes can start with what bonded and seamless construction actually means, see finished builds in the seamless and bonded range, or read how seamless polo construction is specified. The bonding floor covers the seams and routes, and fabric documentation covers what arrives with the material. If you are ready to specify, send your specification for a quote.