PUR hot melt adhesive for footwear is a moisture-reactive adhesive applied in a molten state. It develops handling strength as it cools, then continues curing to build the final bond. A suitable grade can be used for upper laminates, toe puffs, heel counters, insoles, midsoles and selected sole-attaching operations. The words “PUR adhesive,” however, do not prove that one product will bond every leather, fabric, EVA, TPU, PU or rubber compound.
Footwear buyers should approve the complete bond: the exact material pair, surface preparation, adhesive amount, application temperature, assembly delay, pressure, cure condition and finished-shoe test. This guide explains how to define that system and run a production-relevant trial.
When comparing a hot melt adhesive for shoe manufacturing, first confirm whether the supplier means a reactive PUR liquid melt or a thermoplastic film, web or powder. The names are often used loosely, but the processing and test timing are different.
Quick answer
Choose a PUR hot melt adhesive for footwear only after answering four questions:
- Which two commercial materials meet at the bond line?
- Can the adhesive wet both prepared surfaces within the available assembly time?
- Does the joint develop enough early strength for the next production step?
- Does the fully cured shoe pass the required peel, flex, heat, humidity and ageing tests?
PUR can shorten or remove a solvent flash-off stage and may support single-side coating in a validated process. It does not automatically remove the need for roughing, cleaning, priming, controlled pressure or cure time.
Contents
- What PUR hot melt means in footwear
- Map the shoe before selecting an adhesive
- How common shoe materials change the bond
- Why footwear factories choose reactive PUR
- Build a repeatable bonding process
- Match the application method to the component
- Compare technical data without false shortcuts
- Run a three-stage approval trial
- Approval tests for footwear bonds
- Read the failure surface
- Information to send with an RFQ
- Frequently asked questions
What PUR hot melt means in footwear
The term “PU shoe adhesive” is broad. It may refer to a solvent-based polyurethane cement, a water-based PU dispersion, a thermoplastic polyurethane film or a moisture-reactive polyurethane hot melt. These systems do not use the same equipment or approval schedule.
| Adhesive system | How the bond forms | Typical process feature | Main control point |
|---|---|---|---|
| Reactive PUR hot melt | Sets by cooling, then cures with moisture | Molten application with no solvent flash-off | Moisture protection, temperature, open time and cure |
| Thermoplastic PU film, web or powder | Melts or activates under heat and sets on cooling | Preplaced adhesive and heated pressing | Activation temperature, pressure and cooling |
| Water-based PU adhesive | Bonds after water removal and any specified activation or crosslinking | Drying stage before assembly | Drying completeness, activation and pot life if crosslinked |
| Solvent-based PU or contact cement | Bonds after solvent flash-off and, in some processes, heat reactivation | One-side or two-side coating depending on the system | Ventilation, flash-off, activation and surface treatment |
This article focuses on moisture-reactive PUR hot melt. For a broader chemistry overview, see the PUR hot melt adhesive product guide.
Reactive PUR develops its bond in two stages. Cooling provides green strength for handling. Moisture cure then forms a crosslinked network that improves final strength and resistance. The second stage is why a five-minute peel result and a fully cured peel result answer different questions.
Ask the supplier to state the chemistry and product form in writing. A thermoplastic TPU film may be an excellent footwear bonding adhesive, but it should not be approved under a reactive PUR process specification.
Map the shoe before selecting an adhesive
A shoe contains several adhesive joints with different jobs. Start with a bond map instead of one general description such as “sports shoe glue.”
| Bond location | Possible material pair | What the joint must do | Common approval risk |
|---|---|---|---|
| Upper laminate | Mesh, knit or microfiber to foam or lining | Stay soft, breathable and visually clean | Strike-through, stiffness, yellowing or delamination after flexing |
| Toe puff or heel counter | Thermoplastic stiffener to upper material or lining | Hold shape after forming and wear | Short activation window, spring-back or edge lifting |
| Insole or strobel assembly | Textile or nonwoven to insole board, foam or reinforcement | Resist repeated bending and internal moisture | Local dry spots, board tear or bond loss after flexing |
| Midsole lamination | EVA, PU foam, TPU or reinforcement layer | Hold through compression, rebound and temperature change | Mold-release contamination or cohesive foam failure |
| Outsole to upper or midsole | Rubber, TPR, TPU, PU or EVA to prepared upper or midsole | Resist edge peel, flexing, water and heat | Poor surface preparation, short open time or incomplete pressure |
| Labels, overlays and small reinforcements | Film, textile, synthetic leather or foam | Stay located without marking the visible face | Excess adhesive, squeeze-out or heat damage |
The map should name the commercial grade, supplier, color, density, finish and bonding side of each material. “EVA to mesh” is not enough. A change in EVA density, rubber compound, textile finish, recycled content, mold-release agent or backing coating can change the result even when the material name stays the same.
Sole geometry also matters. A flat running-shoe sole can accept roller coating more easily than a deep cupsole or a sole with a high sidewall. Recesses, sharp curves and variable bond-line pressure can turn an approved flat coupon into a poor whole-shoe bond.
How common shoe materials change the bond
The following table is a trial-planning guide. It is not a universal preparation recipe. Confirm any cleaner, primer, roughing depth or surface treatment with the material and adhesive suppliers before production.
A PUR adhesive for shoe materials must be matched to the actual bonding surface and compound rather than a broad label such as leather, rubber or EVA.
| Shoe material | What can interfere with adhesion | Trial checkpoint |
|---|---|---|
| Natural leather | Oils, waxes, variable finish, loose fibers and moisture variation | Test the actual finish and lot; control roughing and dust removal without damaging the leather |
| PU synthetic leather or microfiber | Topcoat chemistry, backing variation, plasticizer or weak coating adhesion | Determine whether failure occurs at the adhesive interface or inside the coating |
| Polyester, nylon, knit and mesh | Water-repellent finish, lubricant, dye treatment, loose construction and heat sensitivity | Check wetting, penetration, stiffness, color change and strike-through |
| EVA foam or molded EVA | Closed surface skin, density, crosslinking, release agent and surface ageing | Compare untreated and approved preparation routes; inspect for foam tear after peeling |
| Molded PU foam or sole unit | Release agent, surface oxidation, cellular structure and hydrolysis history | Verify cleaning or primer needs on fresh and aged production parts |
| TPU component | Grade-specific surface chemistry, processing aid, paint or mold release | Test the exact molded part and any printed or coated area; do not assume all TPU grades behave alike |
| Vulcanized rubber or SBR | Wax bloom, sulfur compounds, mold release and low-energy surface | Control roughing and the specified chemical or plasma treatment; record the time from treatment to bonding |
| TPR or other TPE | Oil, plasticizer, compound variation and low surface energy | Screen migration resistance and the approved primer or treatment |
| PVC component | Plasticizer level, surface contamination and migration during ageing | Run aged peel tests and check for softening, staining or adhesive transfer |
| Insole board and nonwoven | Porosity, dust, absorbed moisture and weak surface fibers | Control coat weight and penetration; distinguish adhesive failure from board delamination |
Surface preparation is part of the approved process, not a repair for an unsuitable adhesive. If a candidate works only after an aggressive treatment that damages the shoe material or slows the line beyond its takt time, it is not a practical match.
Use retained pieces from the same material lots for candidate comparisons. Changing both the adhesive and the outsole lot makes the result hard to interpret.
Why footwear factories choose reactive PUR
Reactive PUR is useful when a shoe joint needs fast handling plus stronger performance after cure. Depending on the formulation and the approved material pair, it can offer:
- good wetting at a controlled molten viscosity;
- early strength as the adhesive cools;
- a flexible bond line for moving components;
- stronger heat, humidity, chemical or plasticizer resistance after full cure;
- precise, repeatable application by roller, slot, bead or automated dispensing equipment;
- lower adhesive use in a validated single-side coating process.
These are formulation-dependent results. A PUR grade chosen for fast crystallization and high green strength may provide less assembly time. A slower-setting grade may suit a complex upper but require longer compression or more support before handling. The viscosity, open time and setting time guide explains why these values must be compared under stated conditions.
Reactive PUR is not always the easiest choice. It needs moisture-resistant packaging, suitable melt equipment, controlled shutdown and cleaning procedures, and a defined cure period. A low-volume hand process, a heat-sensitive decorative layer, an unusually long assembly delay or a repairable bond may favor another adhesive form.
Build a repeatable bonding process
The production window must be wide enough for normal variation. A trial that passes at one carefully adjusted setting can still fail when material temperature drops, an operator takes longer to position a part or the coat weight drifts.
1. Lock the material and preparation route
Record the substrate supplier, product code, lot, bonding side, age and storage condition. Document roughing, cleaning, primer, plasma, corona or other treatment. Include tool type, treatment level and maximum allowed time before bonding where relevant.
Do not describe a sole only as “rubber.” The compound and surface history often matter more than the generic polymer label.
2. Protect the adhesive from moisture before use
Uncured reactive PUR can react with humid air. Inspect the package seal and date code before loading. Use the package-opening, melter and shutdown procedure specified for the grade and equipment. Gel, skin or cured particles can cause unstable flow, blocked filters or weak coverage.
The site’s hot melt adhesive storage and shelf-life guide covers receiving checks, opened-package control and batch traceability.
3. Verify actual adhesive temperature
The melter display is not proof of the adhesive temperature at the roller, slot or nozzle. Check the approved measurement point after the system reaches stable production. Hose length, flow rate, cold components and pauses can change the delivered temperature.
Use the grade-specific processing range. Excess heat can shorten open time through degradation, increase fumes or color change, damage shoe materials and accelerate reaction inside the system. Too little heat can raise viscosity, reduce transfer and leave dry areas.
4. Measure adhesive add-on
Record coat weight in g/m², adhesive mass per part, wet film thickness or another repeatable measure suited to the component. A dial position is not a transferable specification.
Too little adhesive may leave incomplete coverage. Too much can increase squeeze-out, stiffness, cure time and cost without improving the joint. Calculate the resulting cost per pair with the hot melt adhesive consumption and cost guide.
5. Join within the practical open time
Open time begins at deposition. The useful window depends on adhesive temperature, coat weight, substrate temperature, room conditions, component size and heat loss before pressing. Measure the real delay from coating to contact at the fastest and slowest expected operator cycles.
A tacky surface does not prove that the adhesive can still wet the second material. Trial the near and far ends of the proposed window and inspect both peel force and failure mode.
6. Apply pressure to the complete bond area
Pressure must bring the prepared surfaces into intimate contact without crushing foam, distorting the upper or forcing adhesive out of the joint. Record pressure, dwell time, platen or bladder condition and part position. For curved soles, inspect toe, waist, heel and sidewall zones separately.
7. Separate handling release from final cure
Define when the assembly may leave the press, when it may enter the next operation and when it may be tested as fully cured. Moisture availability, bond-line thickness, substrate permeability, temperature and humidity can change cure speed.
Follow the supplier’s written cure schedule and validate it on the actual construction. Detailed operating and cleaning controls are covered in how to use PUR hot melt adhesive.
Match the application method to the component
| Application method | Suitable starting use | What to verify during the trial |
|---|---|---|
| Roller coating | Flat soles, midsoles, stiffeners and cut components | Edge coverage, transfer uniformity, roller temperature, film weight and contamination |
| Slot-die or controlled film coating | Upper laminates, foam, textile and broad-area components | Cross-web profile, strike-through, coat weight and open time after heat loss |
| Bead or dot dispensing | Local reinforcement, labels and small components | Bead placement, compression spread, read-through and unbonded gaps |
| Spray or robotic dispensing | Irregular surfaces and selected three-dimensional parts | Coverage at corners, overspray, pattern repeatability and nozzle stability |
| Pre-coated film, web or powder | Heat-activated cut parts, toe puffs, counters and laminates | Confirm whether the system is reactive or thermoplastic; validate activation, pressure and cooling |
Equipment compatibility includes more than whether the adhesive melts. Confirm pump capacity, hose and seal compatibility, roller or nozzle design, temperature control, filtration, purge or cleaner procedure, shutdown duration and safe operator access.
Single-side coating should be treated as a trial result, not a default promise. A porous material may absorb part of the coating, while a dense molded sole may need separate treatment. The line must still produce complete wetting at the intended interface.
Compare technical data without false shortcuts
Ask for a current TDS and SDS before the trial, then request a lot-specific COA if it forms part of the purchase specification. These documents have different jobs, as explained in the TDS, SDS and COA buyer’s guide.
| Data to request | Minimum context needed |
|---|---|
| Product identity | Reactive PUR chemistry, product form, color and packaging |
| Melt viscosity | Value and range, test temperature, method, spindle and speed where applicable |
| Application range | Recommended tank, hose and applicator settings, plus maximum molten residence guidance |
| Open time | Test substrate, coat weight, adhesive and substrate temperature, room condition and pass criterion |
| Green strength | Time after joining, specimen geometry, conditioning and test method |
| Cure schedule | Time, temperature and humidity or other defined conditioning before final testing |
| Recommended add-on | Range tied to the application method and material pair |
| Bond performance | Material pair, surface preparation, specimen geometry, test method, speed and failure mode |
| Environmental resistance | Heat, humidity, hydrolysis, water, cold or chemical condition and duration |
| Safety and regulatory status | Current SDS, residual monomer information when requested and destination-market documentation |
| Storage and handling | Shelf-life basis, storage range, opened-package procedure and traceable date code |
| Change control | Agreed COA items, batch traceability and notice for formulation, raw-material or site changes |
Apparent viscosity can help predict pumping, transfer and wetting, but values are comparable only at aligned test conditions. If viscosity is a purchase-control item, use the site’s ASTM D3236 viscosity comparison guidance.
Do not approve a footwear adhesive by softening point alone. A reactive PUR continues to cure after cooling, and a softening-point value does not directly predict upper-to-sole adhesion, edge peel, flex durability or heat resistance in the finished shoe.
Run a three-stage approval trial
Write the pass criteria before receiving samples. Keep the current approved adhesive as a control when possible and change one main variable at a time.
Stage 1: Controlled material-pair screening
Prepare coupons from retained production materials. Include every critical material pair and the approved surface treatment. The matrix should cover:
- candidate and control adhesive;
- nominal coat weight plus justified low and high conditions;
- shortest, nominal and longest expected assembly delay;
- normal surface preparation plus realistic boundary conditions;
- early handling test and fully cured test;
- unaged and required aged conditions.
SATRA TM414 can be used when an applicable procedure is required for preparing hot-melt-bonded assemblies for peel testing. Use the buyer’s specified edition and follow the complete method rather than copying a partial online summary.
Stage 2: Pilot-line trial
Run the candidate through the intended melter and applicator. Produce enough components to represent startup, stable running, a planned pause and restart. Record:
| Process item | What to capture |
|---|---|
| Material | Supplier, code, lot, age, temperature and preparation |
| Adhesive | Sample code, batch, package condition and loading time |
| Equipment | Melter, hose, roller or nozzle, pump setting and filter condition |
| Temperature | Setpoints and verified application-point temperature |
| Application | Coat weight or mass per part, pattern and coverage |
| Assembly | Delay to contact, pressure, dwell and release time |
| Environment | Room temperature and humidity |
| Output | Number made, rejects, stops, stringing, gel, smoke, odor or cleaning issue |
The trial should show whether operators can hold the window across production, rather than prove that an engineer can make one good pair.
Stage 3: Finished-shoe and production validation
Produce complete shoes across the agreed sizes, colors, material lots and critical constructions. Size and geometry can change pressure distribution and assembly time. Keep traceable samples for initial, fully cured and aged testing.
Complete the required whole-shoe tests, wearer or fit trials if specified, and a production run long enough to expose temperature drift, adhesive residence time, surface-preparation variation and restart behavior. The general hot melt adhesive sample-testing guide provides a scorecard structure for comparing candidates.
Approval tests for footwear bonds
No single peel result approves every shoe. Build the test plan from the joint’s service conditions and the buyer’s footwear specification.
| Test | What it answers | Important controls |
|---|---|---|
| Application and coverage check | Can the adhesive run and cover the intended area? | Actual temperature, coat weight, pattern and part temperature |
| Green-strength or early peel test | Can the joint survive handling and the next operation? | Exact time after pressing, peel direction and conditioning |
| Fully cured peel or T-peel | Does the material pair develop the required final bond? | Cure condition, specimen width, test speed and failure mode |
| Whole-shoe upper-to-sole adhesion | Does the finished construction resist separation near the sole edge? | Toe, waist, heel or specified zone, construction and conditioning |
| Flex or fatigue test | Does repeated movement start edge lift or delamination? | Flex angle, cycles, environment and inspection interval |
| Heat resistance or heat ageing | Does the bond creep, open or weaken at the required temperature? | Load, temperature, duration and test timing after ageing |
| Humidity, water or hydrolysis conditioning | Does the joint retain strength in wet or humid service? | Water chemistry, temperature, exposure time and recovery condition |
| Cold conditioning and flexing | Does the bond remain flexible and attached at low temperature? | Conditioning temperature, time and test while cold |
| Chemical or sweat exposure | Does the bond tolerate the product’s use environment? | Test solution, contact mode, duration and visual changes |
| Appearance inspection | Does bonding damage the visible shoe? | Strike-through, staining, yellowing, squeeze-out, gloss and distortion |
ISO 17708:2018 describes a method for measuring resistance to upper-to-outsole separation, separation between adjacent outsole layers or failure within the upper or sole. It also includes ageing conditions that can support production control. The method does not create one universal acceptance value for every brand and footwear type.
If a buyer specifies SATRA methods, confirm the current method and issue. SATRA TM401 addresses peel strength of adhesive bonds, TM409 addresses heat ageing and heat resistance of sole bonds in complete footwear, and TM414 covers preparation of hot-melt-bonded assemblies for peel tests. Do not mix specimen preparation from one method with a threshold taken from another report.
For every result, record the force, specimen width, test speed, conditioning, cure age and failure mode. “Passed peel test” is not enough for a transferable approval record.
Set acceptance limits before viewing results
The approval specification should separate four types of requirement:
- Processing window: temperature, coat weight, open time, pressure and dwell limits that production can hold.
- Early performance: minimum handling strength at the time the part enters the next operation.
- Final performance: peel or whole-shoe adhesion after the defined cure condition.
- Retained performance: result after heat, humidity, water, hydrolysis, cold, flexing or chemical exposure required for the shoe.
Set values from the brand specification, product category, risk level, current approved control and agreed test method. Do not copy a generic N/mm figure from a supplier page and treat it as an ISO requirement.
Approve a window rather than a single best setting. The candidate should pass at realistic low and high process limits with an agreed margin. If it passes only at the center point, normal factory variation may cause intermittent failures.
Read the failure surface
Force data tells only part of the story. Photograph both sides after peeling and classify the failure.
| Observed failure | What it may indicate | What to check next |
|---|---|---|
| Clean release from one substrate | Poor wetting, contamination, low surface energy, cooled adhesive or unsuitable treatment | Surface cleanliness, treatment age, primer, interface temperature and open time |
| Adhesive split within the bond line | Low cohesive strength at that test time, incomplete cure, excessive thickness or unsuitable grade | Cure condition, coat weight, formulation and test temperature |
| Tear within foam, leather or textile | Bond is locally stronger than the substrate | Uniformity across specimens and whether the substrate strength meets the shoe requirement |
| Separation inside a coated material | Weak coating, backing or interlayer rather than direct adhesive release | Material construction and supplier lot; do not solve only by adding more adhesive |
| Edge lift after heat or humidity | Marginal surface treatment, cure, pressure or environmental resistance | Aged failure mode, bond-line coverage and process limits |
| Strong final bond but weak early handling | Green strength or setting speed is too low for the line | Release time, compression, part restraint and faster-setting candidate |
| Stringing, skips or unstable coat | Viscosity, temperature, flow, nozzle or roller issue | Verified material temperature, residence time, pump and applicator condition |
| Gel or cured particles | Moisture ingress or excessive residence and shutdown exposure | Package seal, loading method, melter atmosphere and shutdown procedure |
Use a structured cause check before changing the formula. The hot melt adhesive troubleshooting guide can help separate material, process, equipment and storage causes.
Information to send with an RFQ
A footwear-grade request should contain enough detail for the supplier to select a realistic starting product.
- Shoe type, construction method, destination market and expected use
- Exact bond location and a section drawing or clear photo
- Commercial name, supplier and specification for both materials
- Bonding side, surface finish, recycled content and known release agent
- Current roughing, cleaning, primer or plasma process
- Application method, equipment model and available temperature range
- Coat weight or current adhesive use per pair
- Line speed, coating-to-contact delay, pressure and dwell time
- Earliest handling point and required full-cure release time
- Heat, humidity, water, hydrolysis, cold, flex and chemical exposure
- Test methods, specimen conditions and written pass criteria
- Current adhesive, failure mode and reason for changing
- Package size, monthly consumption, storage condition and destination
- Required TDS, SDS, COA, traceability and change notification
The hot melt adhesive RFQ checklist can be used for the commercial and documentation part of the request.
Compare cost per accepted pair, not price per kilogram. Include coat weight, primer or preparation, labor, energy, cure inventory, startup waste, cleaning, rejected shoes and field returns. A higher-priced adhesive may lower the total process cost, but only measured production data can prove it.
Frequently asked questions
Is PUR hot melt adhesive the same as ordinary PU shoe glue?
No. Ordinary “PU shoe glue” may be solvent based or water based. Reactive PUR hot melt is applied molten, gains handling strength as it cools and then moisture cures. Confirm the exact chemistry, product form, equipment and cure schedule.
Can PUR hot melt bond EVA, rubber, TPU, PU, leather and textile?
A suitable PUR grade can bond many of these materials, but the generic material name does not prove compatibility. Compound, finish, release agent, coating, surface treatment and process conditions all affect the result. Test the exact commercial materials and lots.
Can a footwear factory apply PUR to one side only?
Some material pairs and application systems can pass with single-side coating. The process still needs adequate adhesive transfer, surface preparation, wetting and pressure. Approve single-side use through coupon, pilot-line and whole-shoe tests rather than assuming it applies to every sole and upper.
Does reactive PUR remove the need for primer?
Not in every case. Rubber, TPR, EVA, TPU, coated materials and contaminated molded parts may need a specified treatment or primer. The requirement depends on the compound and adhesive. Surface preparation should be part of the approved process record.
What application temperature should be used for shoe manufacturing?
Use the grade-specific TDS and supplier trial recommendation. Verify the adhesive temperature at the application point. A universal temperature can cause poor transfer at the low end or adhesive and substrate damage at the high end.
How long should PUR footwear bonds cure before testing?
Follow the written cure schedule for the candidate and the test method. Record early handling strength separately from final performance. Thick or moisture-restricted bond lines may cure differently from open laboratory coupons.
Which test should approve upper-to-sole bonding?
Use the footwear brand’s specified method and acceptance value. ISO 17708 is a relevant whole-shoe method for upper-to-sole separation. Coupon peel, flexing and environmental ageing are also needed when the product specification calls for them.
Why can a strong laboratory coupon fail on a complete shoe?
The complete shoe adds curves, sidewalls, variable pressure, longer assembly delays and several material interfaces. It may also use different lots or carry mold release and roughing dust. Pilot-line and whole-shoe validation expose those differences.
Is PUR hot melt a zero-VOC and risk-free process?
Reactive PUR hot melt is commonly supplied as a 100% solids, solvent-free adhesive, so it does not need the solvent flash-off used by many contact cements. Uncured PUR still requires the controls stated in the current SDS, including controls for heat and reactive isocyanate chemistry. Review worker training, ventilation, closed equipment and destination-market rules before approval.
Can cured PUR be reheated and reused?
Fully cured reactive PUR does not remelt like a standard thermoplastic hot melt. Moisture-cured material in filters, hoses or nozzles can create blockages. Follow the adhesive and equipment suppliers’ loading, shutdown and cleaning procedures.
Send a complete footwear trial brief
For a useful grade recommendation, send the actual upper, midsole and outsole samples together with the bond map, preparation route, equipment details and test requirements. KAISUN can then propose a starting PUR hot melt adhesive and a controlled trial window for the specified footwear materials.
Keep the final approval tied to the material codes, surface preparation, process limits, cure condition and test methods. That record gives purchasing, production and quality teams the same definition of an approved footwear bond.
