DWR Coating vs PU Lamination vs TPU Composite: What Is the Best Fabric for Waterproofing?

In bag procurement and product development, “waterproofing” is one of the most frequently mentioned yet most easily misunderstood performance indicators. End consumers often use “whether it is waterproof” as the key criterion for judgment, but professional bag manufacturers understand that waterproof performance is actually a graded spectrum — ranging from surface treatments that can only resist minor splashes to composite barriers capable of withstanding water immersion. Different processes correspond to completely different technical approaches, cost structures, and application scenarios.

Currently, the three most widely used waterproof finishing technologies in the bag industry are: DWR Durable Water Repellent Coating, PU Polyurethane Coating/Lamination, and TPU Thermoplastic Polyurethane Lamination.

They are not simply a linear hierarchy of “good” and “better.” Instead, each technology represents a different solution with its own trade-offs among waterproof rating, breathability, hand feel, durability, and cost. For backpack OEM buyers, understanding the fundamental differences between these three technologies is essential for developing reasonable product specifications, controlling costs, and meeting end-user expectations.

This article will provide a systematic comparison of these three waterproof finishing technologies from three perspectives: process principles, performance data, and manufacturing practices, offering an objective reference for material selection decisions in the bag industry.

Table of Contents:

• Process Principles 
• Performance Data Comparison 
• Selection Recommendations for Bag Manufacturing 
• Waterproof Performance Testing Standards and Interpretation 
• Frequently Asked Questions 
• Conclusion 

Ⅰ.  Process Principles

1.1  DWR Coating

1.1.1 Technical Principle: Making Water Droplets “Stand” on the Fabric

DWR (Durable Water Repellent) is a chemical finishing process applied to the surface of fabric, rather than a structural waterproof layer. It works by changing the surface tension characteristics of the fibers, causing water molecules to form droplets on the surface of the fabric and roll off, rather than wetting and penetrating into the gaps between the yarns.

It is important to clarify that DWR does not make the fabric waterproof. It cannot prevent water penetration under continuous water pressure, nor can it seal the pores of the textile itself. A canvas or nylon fabric treated only with DWR typically achieves a hydrostatic head value of just 300–600 mm in the Hydrostatic Head Test, which means it can only cope with light splashes or brief periods of drizzle.

1.1.2 Core Advantages: Lightweight, Breathability, and Quick Drying

The core advantage of DWR lies in the fact that it has almost no impact on the original properties of the fabric. Since the coating is extremely thin (typically at the micron level), the fabric’s hand feel, softness, breathability, and weight are barely affected. For foldable bags, lining materials, or summer commuter backpacks that pursue an “ultralight” design, DWR is an ideal choice. It can also significantly reduce the amount of moisture absorbed by the fabric, allowing the bag to dry faster in humid environments and reducing the burden caused by increased weight as the fabric absorbs water.

In the production practice of Outdoor Waterproof Backpack OEM, DWR is often used as the “first layer of protection.” It reduces the amount of water reaching the underlying waterproof barrier, thereby indirectly extending the service life of the PU or TPU waterproof layer. For example, in an outdoor backpack featuring a three-layer construction of “ripstop nylon + DWR surface + PU backing,” the presence of DWR means that the PU coating does not have to bear the full impact of surface moisture on its own.

1.1.3 Limitations: Durability Bottlenecks and Maintenance Costs

The biggest drawback of DWR is its durability. As time goes by, dirt, oils, detergent residues, and repeated bending and abrasion on the fabric surface can all damage the hydrophobic molecular layer of DWR. Consumers often have this experience: when a backpack is new, water droplets roll off it like water on a lotus leaf in the rain, but after six months of use, the fabric begins to become wet and absorb water. This does not mean that the fabric is “leaking”; rather, the failure of the DWR treatment allows water to directly wet and penetrate the interior of the textile.

Maintaining DWR requires end users to periodically reapply a DWR restoration treatment, which increases the product’s overall cost of use to some extent. For brands, this means that the limitations of DWR need to be clearly explained in the product instructions to avoid a gap between “waterproof” claims and actual performance.

1.1.4 Environmental Transition: The Shift from C8 to C0 and Fluorine-Free Formulations

The DWR industry is undergoing a profound environmental transformation. Traditional DWR formulations were often based on fluorinated compounds (PFAS), such as C8 or C6 fluorocarbon chains. These substances are extremely chemically stable and are known as “Forever Chemicals.” They can accumulate in the environment and living organisms, raising serious ecological and health concerns.

EU REACH regulations, restrictions imposed by the U.S. EPA, and the sustainability commitments of major outdoor brands are driving the transition from fluorinated DWR formulations to fluorine-free formulations (C0 or PFAS-free). Fluorine-free DWR treatments are based on hydrocarbons or siloxanes. Although they are somewhat inferior to traditional fluorinated products in terms of oil and grease resistance and long-term durability, they are now capable of meeting the requirements of most bag applications.

1.2  PU Lamination

1.2.1 Technical Principle: Sealing Fabric Pores by Converting Liquid into a Solid

PU (Polyurethane) lamination is the most widely used waterproof finishing process in the bag industry.

Unlike the surface treatment provided by DWR, PU waterproofing involves directly applying a liquid PU coating to the back side (reverse side) of the fabric. After the coating cures, it forms a strong yet flexible polymer film that adheres to the textile substrate. This PU film fills the gaps between the interlaced points of the fabric, thereby preventing liquid water from penetrating through.

The thickness of a PU coating is typically measured by “coating weight” or “wet film thickness.” The greater the coating weight, the stronger the waterproof performance; however, the fabric will also become correspondingly stiffer and heavier. A piece of 210D nylon combined with a standard PU coating (approximately 30 g/m²) can typically achieve a hydrostatic head value of 1,000–2,000 mm, which is sufficient to handle moderate rain in everyday commuting environments.

1.2.2 Core Advantages: The Balanced Choice in Terms of Performance

• The reason PU lamination has become the mainstream choice in the industry is that it achieves an “acceptable balance” across multiple key performance indicators:
• Waterproofing: PU coating provides a substantial waterproof barrier, far exceeding the water-repellent effect of DWR. For travel backpacks, everyday commuter bags, and general outdoor bags, PU-coated fabric offers an optimal balance between cost and performance.
• Hand Feel and Processability: Fabric with a PU coating still retains a certain degree of softness and offers good sewability and processing performance.
• Cost: The additional cost of PU coating is relatively moderate and is significantly lower than that of TPU lamination.
• Supply Chain Maturity: At the same time, PU lamination is supported by mature production processes, low supply-chain barriers, readily available stock, and more controllable lead times, making it highly suitable for production planning for large-volume orders.

1.2.3 Limitations: Insufficient Durability and Breathability

However, PU coating also has several significant drawbacks that cannot be overlooked:

• Hydrolysis Risk: The ester bonds in the PU molecular chains are susceptible to moisture attack in hot and humid environments, resulting in a hydrolysis reaction. This can cause the coating to powder, peel off, or become sticky. The severity of this issue is closely related to the PU formulation (polyether-based vs. polyester-based), the temperature and humidity of the operating environment, and storage conditions.
• Reduced Breathability: While PU coating seals the pores of the fabric, it also significantly reduces the fabric’s water vapor transmission rate.
• Low-Temperature Embrittlement: Traditional PU gradually becomes harder in low-temperature environments and, in extreme cases, the coating may crack. This represents a potential risk for backpacks intended for outdoor use during winter.

1.3  TPU Composite

1.3.1 Technical Principle: A Seamless Barrier Made from Thermoplastic Elastomer

TPU (Thermoplastic Polyurethane) composite technology represents a higher level of waterproofing technology for bag fabrics. Unlike the “coating and film-forming” process used for PU coating, TPU lamination involves firmly bonding a pre-formed TPU film to the fabric substrate through hot-melt adhesive or heat-pressing, creating an independent, continuous, and uniformly thick waterproof barrier.

TPU itself is a block copolymer that combines the high elasticity of rubber with the processability of plastic. The hard segments in its molecular chains (composed of diisocyanates and chain extenders) provide strength and temperature resistance, while the soft segments (composed of long-chain polyols) provide flexibility and elasticity. This unique structure allows TPU film to remain flexible across a very wide temperature range (-40°C to +80°C), without becoming brittle at low temperatures or softening and becoming sticky at high temperatures like PU coatings can.

1.3.2 Performance Advantages: Comprehensive Protection at a Higher Level

• Superior Waterproofing: TPU composite fabrics typically achieve a hydrostatic head value of 3,000–5,000 mm, or even higher, making them capable of withstanding extreme conditions such as heavy rain and water immersion. For diving bags, canyoning bags, water sports equipment, and high-end outdoor backpacks, TPU lamination provides the technical foundation for achieving “true waterproofing” rather than simply “rain resistance.”
• Excellent Durability: TPU offers significantly better resistance to hydrolysis, UV exposure, oils, and chemicals than PU.
• Weldability: The thermoplastic properties of TPU allow seamless connections to be achieved through High-Frequency (HF) Welding or Hot Air Welding. This means that a bag factory can manufacture completely needle-hole-free waterproof bags, elevating waterproof performance from the “fabric level” to the “structural level.”
• Elasticity and Hand Feel: TPU film has a lower elastic modulus than PU coatings. Therefore, even after lamination, the fabric can maintain high strength while retaining good flexibility and resilience.

1.3.3  Limitations: Cost and Processing Challenges

The main drawbacks of TPU lamination are concentrated in its cost and manufacturing complexity.

• Material Cost: TPU film itself is more expensive than PU resin. Combined with the equipment investment and energy consumption required for the lamination process, TPU laminated fabric typically costs 1.5 times or more than PU-coated fabric of the same specification. For bags targeting price-sensitive mass markets, this cost increase may directly determine the product’s market positioning.
• Higher MOQ: There are very few standard TPU specifications available from stock, and most require customization. Except for standard black and white colors, which can be customized with a relatively low MOQ, other colors generally have a minimum order quantity of around 1,000 yards.
• Processing Requirements: TPU laminated fabrics have more demanding sewing requirements. When pierced by a needle, TPU film is prone to the “needle-hole effect.” Although the needle holes themselves are very small, they can become pathways for water penetration under high water pressure. Therefore, Backpack OEM orders using TPU fabric usually need to incorporate seam tape or welding processes to seal the needle holes.
• Breathability Limitations: Although TPU can be manufactured into microporous breathable films (using a principle similar to Gore-Tex), most TPU laminated fabrics used for bags employ dense, non-microporous films in order to maximize waterproof performance. This means their breathability is generally lower than that of PU-coated fabrics, resulting in a higher risk of condensation forming inside the bag.

II. Performance Data Comparison of the Three Waterproofing Processes

To provide a more intuitive understanding of the differences among the three processes, the following table presents a quantitative comparison across multiple key dimensions:

In summary, the three processes show a clear stepwise difference in waterproofing performance:

• DWR-treated fabrics will eventually allow water to penetrate the textile structure during prolonged rainfall; 
• PU-coated fabrics can block liquid water, but may leak under high water pressure or where the coating has been damaged; 
• TPU laminated fabrics can provide a reliable waterproof barrier in the vast majority of non-immersion applications. 

For Rucksack OEM manufacturers, this means that waterproof specifications must be established according to the product’s actual usage scenarios, rather than blindly pursuing the highest possible numerical rating.

III.  Selection Recommendations for Bag Manufacturing

3.1 Backpack

Backpacks are one of the product categories where all three waterproofing processes are most widely applied, because backpacks with different market positions have vastly different waterproofing requirements.

• Urban Commuter Backpacks (20L–30L) typically use a combination of “PU coating + DWR surface treatment.” Rainfall in urban environments is generally short-duration and moderate, making PU coating sufficient for most situations; DWR helps maintain a dry, clean, and attractive appearance on the fabric surface. This combination achieves an optimal balance among cost, performance, and hand feel, making it a standard configuration for backpack suppliers producing mid-range commuter backpacks.

• Outdoor Hiking Backpacks (40L–65L) face more demanding environmental challenges. The outer fabric may use ripstop nylon + DWR, while high-wear areas such as the bottom and side pockets may use TPU laminated fabric or a thickened PU coating. Some high-end technical backpacks add a TPU laminated waterproof liner inside the main compartment (similar to a dry-bag construction), creating a dual layer of protection: “rain protection on the outside, waterproofing on the inside.”

• Water Sports Bags / Diving Bags must meet genuine waterproofing standards. These products typically use fully TPU-laminated fabric, combined with welded seams, water-resistant zippers (such as YKK Aquaguard), and a Roll-Top Closure design. For these types of products, the production line at a bag factory needs to be equipped with high-frequency welding equipment rather than relying on traditional sewing machines.

3.2 Handbags and Purses

The waterproofing requirements of handbags and purses are often less apparent, but they are equally important.

• Business Handbags focus on appearance and texture. They typically use leather-textured fabrics with PU coating or high-density polyester, combined with a DWR surface treatment. Since business scenarios rarely involve heavy rain or immersion, the waterproofing capability provided by PU coating is more than sufficient.

• Fashion Handbags for Women can use a lighter DWR treatment, or even rely solely on the fabric’s high-density weave to slow down moisture penetration. This is because the waterproofing requirements of fashion handbags are typically limited to “accidental splashes,” while overly heavy coatings can compromise the fabric’s delicate hand feel.

• Travel Bags and Sports Bags tend to favor PU or TPU solutions because they need to cope with unpredictable liquid exposure in a variety of environments, including airports, train stations, and gyms. In particular, the bottom area can be reinforced with TPU laminated fabric, which not only improves abrasion resistance but also effectively prevents water stains and moisture from the ground from penetrating into the bag, thereby extending the service life of the bag.

• Beach Bags are primarily used for short-term outdoor leisure activities and often come into contact with wet sand on the beach and splashes of seawater from swimming pools. Therefore, they typically use a TPU laminated waterproofing solution, which can effectively prevent water and moisture from penetrating and soaking personal belongings. At the same time, the TPU laminated layer also makes it easier to quickly clean off sand particles and salt residue afterward. 

3.3 Cosmetic Bags and Toiletry Bags

Cosmetic bags and toiletry bags are among the smallest bag categories, but their waterproofing requirements are particularly unique. Unlike backpacks and handbags, which primarily need to deal with “external rainwater,” the main threat for cosmetic bags comes from internal leakage. A bottle of foundation that tips over, a tube of sunscreen that bursts under pressure, or a leaking bottle of perfume can ruin all the items inside the bag and may even damage other belongings packed in the same suitcase. Therefore, the waterproofing logic of cosmetic bags and organizer bags is “from the inside out.”

• Cosmetic Bags:

For Cosmetic Bag OEM manufacturers, the fabric selection for cosmetic bags needs to meet three requirements simultaneously: refined appearance, leak protection on the inside, and easy cleaning.

The outer fabric typically uses a DWR surface waterproof treatment, which preserves the fabric’s glossy appearance and delicate hand feel while also providing protection against splashes from bathroom sinks.

The layer that truly takes on the primary waterproofing responsibility is the lining layer. Mid-range cosmetic bags commonly use a “PU-coated lining” construction. This approach keeps costs under control and effectively prevents liquid penetration, but after prolonged use, the lining may swell or undergo surface degradation due to exposure to oils, essential oils, and alcohol-based ingredients found in cosmetics.

Some high-end products instead use a TPU laminated lining, which offers significantly better chemical resistance than PU. It provides stronger resistance to essential oils and alcohol-based cosmetics and can also be made into a seamless inner liner through high-frequency welding, completely eliminating the risk of leakage through needle holes.

• Toiletry Bags

Compared with cosmetic bags, toiletry bags are closer to the positioning of a “soft waterproof case.” Since they directly carry liquid personal-care products, TPU laminated fabric + water-resistant zipper + roll-top closure has become a standard configuration for high-end products.

TPU’s hydrolysis resistance is particularly important in this application. Toiletry bags are often used in high-humidity environments such as bathrooms, where the aging rate of PU coatings can accelerate significantly. For Toiletry Bag OEM buyers targeting European and American markets, toiletry bags made with TPU laminated fabric can not only pass more stringent waterproof tests (such as IPX4 splash-water testing) more easily, but also have a greater chance of receiving positive “leak-proof” feedback from customers based on their actual user experience.

IV.  Waterproof Performance Testing Standards and Interpretation

In custom communication within the bag industry, “waterproof” is an overused and often ambiguous term. After understanding the conventional waterproofing processes, let us now look at the standardized tests used in the industry to define and verify waterproof performance.

4.1  Hydrostatic Head Test

The Hydrostatic Head Test is the most basic and widely used method for measuring a fabric’s resistance to liquid water penetration. The test principle involves securing a fabric specimen onto a fixture with a standardized test area, then applying water pressure to one side of the fabric at a constant rate and recording the pressure height at which water penetrates through to the opposite side of the fabric (measured in millimeters of water column, mm H₂O).

The major standards include:

l AATCC 127 (American Association of Textile Chemists and Colorists): The test pressure increases at a rate of 60 mbar/min, and the method is suitable for routine evaluation of most bag fabrics.

l ISO 811 (International Organization for Standardization): Similar in principle to AATCC 127, but with slightly different pressurization rates and specimen dimensions. European customers typically require test reports based on this standard.

l JIS L 1092 (Japanese Industrial Standard): Widely used throughout Asian supply chains. Method A is the low-pressure method, while Method B is the high-pressure method. High-end outdoor bags often require Method B data.

4.2  Spray Test

The Hydrostatic Head Test measures a fabric’s resistance under static pressure, but in actual use, rainwater comes into contact with the surface of a bag through dynamic impact. The Spray Test is designed to simulate this scenario.

l AATCC 22 and ISO 4920 are the most commonly used spray test standards. During testing, 250 mL of water is sprayed from a fixed height (typically 150 mm) onto a fabric specimen positioned at a 45° angle. The specimen is then evaluated by comparing the wetted area on its surface with a standard wetting rating scale from 1 to 5, with 5 being the best rating.

l The core value of DWR coating is most clearly demonstrated in the Spray Test. A nylon fabric treated with a high-quality DWR finish will cause water droplets to roll off after spraying, leaving almost no wetting on the specimen surface and potentially achieving a 4–5 rating. By contrast, the same fabric after DWR failure will allow water to spread rapidly across the surface and penetrate into the textile structure, potentially resulting in a rating as low as 1–2.

4.3  Rain Test

Both of the tests above use fabric as the test subject, but the ultimate waterproof performance of a bag depends on the systematic performance of “fabric + construction.” The Rain Test (AATCC 35) places the entire bag or sewn fabric assembly in a simulated rainfall environment, spraying water at a specified angle and flow rate to evaluate leakage at structurally vulnerable areas such as seams, zippers, and corners.

A TPU laminated fabric may have a hydrostatic head value as high as 5,000 mm, but if the seams are not sealed with seam tape after sewing, water may first penetrate through the seams during the rain test. Therefore, the Rain Test serves as a bridge connecting “material performance” with “finished-product performance.”

4.4  Moisture Vapor Transmission Rate

In the outdoor backpack sector, consumers often discuss “waterproofing” and “breathability” as opposing characteristics. However, these two properties need to be quantified through different tests. Moisture Vapor Transmission Rate (MVTR) measures a fabric’s ability to allow water vapor to pass through, typically expressed in g/m²/24h.

l ASTM E96 (Cup Method) and JIS L 1099 (Calcium Chloride Method / Moisture Permeability Cup Method) are the major testing standards.

l DWR-treated fabrics have the highest MVTR, generally close to that of the original untreated fabric; PU coatings significantly reduce moisture vapor transmission; and TPU laminated fabrics using dense, non-microporous films typically have the lowest MVTR.

4.5  Reading Test Reports and Applying Them to Quality Control

A qualified waterproof fabric test report should contain at least the following information:

• Test standard and method number (e.g., AATCC 127-2017) 
• Test conditions (temperature, humidity, and pressurization rate) 
• Specimen description (fabric specifications, coating/lamination type) 
• Test results (raw data and ratings) 
• Testing laboratory qualifications (CNAS, CMA, or an internationally recognized third-party laboratory) 

In actual production, manufacturers should implement an incoming material inspection system. When fabric enters the warehouse, hydrostatic head should be sampled and tested according to AATCC 127. This pre-production material verification can identify waterproofing failure risks at an early stage of manufacturing and prevent large-scale rework.

In this regard, Synberry Bag, a source factory specializing in bag manufacturing for 30 years, conducts standardized waterproof testing to confirm performance parameters before each new product is launched, ensuring that the waterproof performance of the final delivered products remains stable and meets customer order requirements, while avoiding customer complaints caused by missing testing procedures.

Image showing SYNBERRY BAG conducting hydrostatic pressure tests on each batch of waterproof materials before launching new products.

V. FAQ

Q1: What is the difference between PVC waterproofing and PU waterproofing?

A: PVC (Polyvinyl Chloride) and PU (Polyurethane) are two completely different polymer systems, and they differ significantly in waterproofing applications for bags.

• Chemical Structure and Environmental Performance: PVC contains chlorine in its molecular chain and requires the addition of plasticizers (such as phthalates) and stabilizers (which may contain heavy metals) during production. When incinerated, it may release harmful substances such as dioxins. EU REACH regulations impose strict restrictions on phthalates and heavy metals in PVC products, and some countries have already restricted the use of PVC in food-contact products and children’s products. PU does not contain chlorine and offers greater formulation flexibility. Water-based PU has significantly better environmental performance than solvent-based PVC.
• Hand Feel and Low-Temperature Performance: PVC film tends to have a relatively stiff hand feel and a strong plastic-like feel. In low-temperature environments (below 0°C), it becomes noticeably harder and may even become brittle, making it prone to creasing or cracking when bent. PU coatings and TPU films remain flexible at low temperatures, making them more suitable for bags that require frequent bending or are intended for use in cold regions.
• Waterproofing and Durability: PVC offers excellent waterproofing, with hydrostatic head values easily exceeding 10,000 mm. However, PVC’s hydrolysis resistance is actually inferior to that of TPU. Long-term exposure to oils or high temperatures may cause plasticizer migration and surface stickiness. PU offers a moderate level of waterproofing (1,000–3,000 mm) but carries a risk of hydrolysis; TPU, meanwhile, offers overall superior performance to both PVC and traditional PU in terms of waterproofing, hydrolysis resistance, and low-temperature toughness.

Q2: Can consumers restore DWR after it fails?

A: Yes, but the effectiveness is limited. DWR is a surface treatment, and once it loses effectiveness, it can be restored using commercially available DWR sprays (such as Nikwax TX.Direct or Grangers).

The restoration process typically involves: cleaning the fabric → low-temperature tumble drying or ironing to activate the fibers → evenly applying a DWR restoration treatment → applying low-temperature heat again to cure the treatment. However, self-restoration is generally less effective than factory-level pad application or spraying processes, and frequent restoration may alter the fabric’s hand feel.

Q3: Is there any way to remedy PU coating that has undergone hydrolysis and become sticky?

A: Once PU coating has undergone obvious hydrolysis (surface stickiness, powdering, or peeling), it constitutes irreversible chemical degradation and cannot be repaired through simple cleaning or recoating.

For brands, prevention is better than remediation. During the procurement stage, bag factories should be required to use hydrolysis-resistant PU, with polyether-based formulations preferred over polyester-based formulations. During storage, warehouse temperature and humidity should also be controlled, with a recommended relative humidity below 60% and temperature below 25°C. For inventory products showing early signs of hydrolysis, isolation and evaluation of the scrap rate are the only appropriate quality-control measures.

Q4: Can the three waterproofing processes be used together?

A: Yes, and this is very common in actual production. A typical “sandwich” construction consists of: DWR water repellency on the face of the fabric → PU coating or TPU lamination on the back of the fabric → seam tape sealing at the seams.

This combination is not simply an addition of performance; rather, the functions are complementary: DWR reduces the amount of water reaching the waterproof barrier and extends the service life of the PU/TPU layer; PU/TPU provides the actual waterproof barrier; and seam tape eliminates structural leakage.

For brands, however, combining multiple solutions significantly increases both cost and process complexity, so whether it is worthwhile should be determined according to the product’s market positioning.

Q5: Is TPU laminated fabric really more environmentally friendly than PU-coated fabric?

A: From a material-property perspective, TPU is a thermoplastic material and can theoretically be recycled and reprocessed, whereas PU coating is a thermosetting/reactive system that becomes difficult to separate and recycle once cured.

However, “more environmentally friendly” is a full-life-cycle question. TPU laminated fabric requires more energy during production, and the composite structure of TPU and fabric also makes actual recycling more difficult.

For brands, rather than focusing excessively on “which one is more environmentally friendly,” it is more practical to clearly restrict harmful substances (such as PFAS, phthalates, and heavy metals) in procurement contracts and prioritize suppliers that have obtained relevant environmental certifications.

Q6: Are waterproof zippers necessary? Can ordinary zippers with storm flaps replace them?

A: This depends on the product’s target waterproofing level. Ordinary zippers have gaps between their teeth, which may allow water to penetrate once hydrostatic pressure exceeds 300–500 mm. Waterproof zippers (such as YKK Aquaguard and Vislon waterproof series) use PU-coated zipper teeth or TPU-laminated zipper tapes to raise the waterproof performance of the zipper area to a level comparable to that of the fabric.

An external Storm Flap can provide a certain degree of protection against rainwater, but it cannot adequately handle strong wind-driven rain or liquid contact when the bag is turned upside down. For commuter bags positioned at the “rain-resistant” level, a storm flap + ordinary zipper is a cost-effective solution. For diving bags or canyoning bags positioned at the “waterproof” level, a waterproof zipper or Roll-Top Closure is a structural element that cannot be compromised.

Conclusion

DWR coating, PU lamination, and TPU composite technology together form a complete technical spectrum in the bag industry, ranging from “water repellency” to “waterproofing.” There is no absolute hierarchy of advantages and disadvantages among them; rather, the key lies in how well each technology matches the product’s positioning, usage scenario, cost budget, and environmental requirements.

As waterproofing technology continues to evolve, DWR is becoming more environmentally friendly, PU is becoming more durable, and TPU is becoming lighter and thinner. As a key link in the bag manufacturing chain, we have always maintained close attention to these technological developments, helping brands transform advances in materials science into greater competitiveness for their end products.

	Author