Polyurethane Dispersion (PUD) is polyurethane in the form of a water-based dispersion rather than a solution—the polyurethane particles are dispersed and stabilized in the aqueous phase, then form a film as the water evaporates. PUD is widely used as a binder and film former in coating, varnish, and water-based finishing formulations.

Because water is used as the dispersion medium, PUD is one of the options for water-based polyurethane or waterborne polyurethane formulations. However, not all PUDs produce the same film characteristics.

The selection of PUD grade and formulation can affect the final result, ranging from matt and soft feel to glossy, hard films with higher mechanical and chemical resistance. So, why can the resulting film characteristics differ? Let’s understand how PUD forms a film and the factors that influence its final properties.

What Is Polyurethane Dispersion (PUD)?

Simply put, polyurethane dispersion (PUD) is polyurethane that is not fully dissolved in water, but instead exists as polyurethane particles dispersed within the water phase.

This is where the term dispersion becomes important.

In a solution, the material used is dissolved in a solvent. In simple terms, the molecules of the material are spread at a molecular level within the medium, forming a homogeneous solution.

In a dispersion, on the other hand, the material exists as small particles spread throughout the carrier medium. In PUD, polyurethane particles are dispersed in water.

System

Process

Result

Solution

Material dissolves in a solvent

Homogeneous solution

PUD (Dispersion)

Polyurethane dispersed as particles, water as the dispersion medium

Polyurethane dispersion

Water is used as the continuous phase because PUD coatings are designed so that polyurethane particles remain stably dispersed in the water phase. Once applied to a surface, the water evaporates and the polyurethane particles undergo film formation.

Because of this, the terms water-based polyurethane and waterborne polyurethane are often used to describe polyurethane systems that use water as their main medium. However, the term water-based doesn’t automatically mean a product is free of every type of solvent or co-solvent — actual composition still depends on the grade and formulation design.

What Are the Basic Components of PUD?

Without going too deep into polymer chemistry, a PUD system generally consists of:

•             Polyurethane polymer, which determines much of the final film’s characteristics.

•             Water, as the continuous phase or dispersion medium.

•             Supporting components, depending on product design and application needs — for example, stabilizers or other materials that help dispersion characteristics and film formation.

The type of polyurethane, polymer structure, particle size, solid content, and the polymer’s surface characteristics all influence how a PUD behaves during application and drying.

That’s why not all PUDs deliver the same result. Two products both classified as polyurethane dispersion can differ significantly in gloss, hardness, flexibility, adhesion, feel, chemical resistance, and film formation.

In other words, PUD is not a single material with one fixed characteristic, but a group of materials that can be engineered for different application needs.

How Does PUD Form a Film?

One reason PUD is widely used as a binder is its ability to form a film after being applied to a substrate.

The process can be understood through a few simple stages.

1. PUD is applied to the substrate PUD is first applied to the target surface — for example, plastic film, cardboard, or a wood surface. At this stage, the polyurethane is still in the form of particles dispersed in water.

2. Water begins to evaporate As the coating starts to dry, water gradually evaporates from the layer. As the water decreases, the distance between polyurethane particles becomes smaller.

3. Polyurethane particles move closer together Particles that were previously spread throughout the water phase begin to move closer and pack more tightly. Drying conditions, temperature, humidity, coating thickness, and PUD characteristics can all affect this process.

4. Particles undergo coalescence In the next stage, polyurethane particles undergo coalescence — the process where the particles merge to form a more continuous layer.

5. A polyurethane film is formed After film formation is complete, a polyurethane layer is formed that adheres to the substrate surface.

In short:

PUD in water → applied → water evaporates → particles move closer → coalescence → polyurethane film forms

This film formation process is critical because it affects the coating’s final characteristics, including:

•             Appearance

•             Gloss or matt

•             Surface feel

•             Tack

•             Adhesion

•             Hardness

•             Flexibility

•             Transparency

Because of this, selecting a PUD shouldn’t be based solely on the “waterborne polyurethane” label. Formulators also need to evaluate how the grade forms a film on the intended substrate and under the actual process conditions.

What Is PUD’s Function in a Formulation?

In a formulation, PUD can serve several main functions. Its most fundamental role is as a binder and film former.

1. PUD as a Binder

As a binder, PUD helps bind the components in a formulation together and forms a layer after drying.

A binder is essentially one of the main components that determines how a coating adheres to and forms a film on a substrate.

Because polyurethane characteristics can be engineered through polymer selection, PUD can be used to design formulations for different performance needs.

2. PUD as a Film Former

PUD also functions as a film former — a material that forms a continuous layer after water evaporates and the polyurethane particles undergo coalescence.

The film’s character can be engineered for a specific application. For instance, a formulation might require a film that is matt, glossy, smooth, soft, hard, flexible, transparent, or has a particular type of resistance.

However, it’s important to understand that not every PUD has all of these characteristics. The final result strongly depends on the type of PUD, the combination of formulation ingredients, the substrate, the application method, and drying conditions.

3. Delivering Surface Characteristics

Selecting the right PUD can also help determine the surface characteristics of a polyurethane coating. Depending on the grade and formulation, PUD can be used to achieve:

•             Matt or gloss finish

•             Soft feel

•             Smooth surface

•             Silky or velvet touch

•             Transparency

•             Low tack or dry surface feel

For example, some PUDs are inherently designed to produce a matt effect, reducing the need for additional matting agents. Conversely, other grades may be chosen when a formulation requires gloss, clarity, hardness, and higher mechanical or chemical resistance.

4. Supporting Water-Based Formulation Development

PUD is relevant for formulators developing water-based polyurethane systems because water serves as the main medium.

Using a waterborne system can be part of a formulation strategy to reduce dependence on solvent-based systems, although performance, VOC, drying, and co-solvent needs still need to be evaluated at the specific formulation and product level.

PUD is therefore not simply a “solvent-based polyurethane replacement.” Formulators need to adjust the entire system to achieve the right film formation, adhesion, appearance, and durability.

Bahtera Adi Jaya Supplies the Esacote PUD Line from Lamberti

PUD performance depends heavily on the grade selected. PT Bahtera Adi Jaya (BAJ) supplies the Esacote line from Lamberti, including Esacote PU 980, Esacote PU 9510, and Esacote PU 77 — each with different binder and film-former characteristics, ranging from inherently matt to high gloss with high hardness.

As a specialty chemicals distributor with a 800+ product portfolio, BAJ is supported by an application lab and technical team to help formulators select the right PUD grade for their application. A full breakdown of each grade, its characteristics, and how to select one based on substrate and target finish is covered in the PUD application article.

FAQ: What You Should Know About PUD Fundamentals

Q1. What is Polyurethane Dispersion?

Polyurethane Dispersion, or PUD, is polyurethane in the form of particles dispersed in water. PUD is widely used as a binder and film former in water-based coating, varnish, and finishing formulations.

Q2. What is PUD’s function in a formulation?

Its main function is as a binder and film former. Once applied and the water evaporates, the polyurethane particles undergo coalescence and form a film on the surface. The resulting film characteristics depend on the type of PUD and the formulation.

Q3. What’s the difference between PUD and solvent-based polyurethane?

The main difference is the medium used in the system. In PUD or waterborne polyurethane, water is the main medium in which the polyurethane is dispersed. In solvent-based polyurethane, the polyurethane exists within an organic solvent-based system.

This difference can affect VOC profile, drying process, film formation, handling, compatibility with formulation components, and production facility requirements.

However, it’s important not to automatically equate waterborne with zero-VOC or solvent-free. That status must be checked against each product’s and formulation’s specific data.

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