How to Test the Antimicrobial Performance of Materials

When manufacturers add an antimicrobial agent to a material, one important question remains:

Does the treatment actually work?

Antimicrobial performance cannot be determined simply by looking at the treated material. Laboratory testing is normally required to evaluate whether a treated material can inhibit or reduce the growth of target microorganisms under defined test conditions.

For manufacturers of textiles, plastics, coatings, rubber products, wood, leather, and other materials, antimicrobial performance testing can help verify product performance, compare formulations, optimize treatment levels, and support technical documentation.

However, there is no single test method that is suitable for every material or application.

The appropriate testing approach depends on the material, antimicrobial technology, target microorganisms, application method, and intended use of the finished product.

1. Why Is Antimicrobial Performance Testing Important?

An antimicrobial agent may perform differently depending on how it is incorporated into or applied to a material.

For example, an antimicrobial treatment used on textile fibers may behave differently from one incorporated into a plastic polymer. A coating formulation may also require a different evaluation approach from a treated wood product.

Testing can help manufacturers determine:

• Whether the treated material shows measurable antimicrobial activity
• How effective the treatment is against selected microorganisms
• Whether different treatment concentrations produce different results
• Whether antimicrobial performance remains after washing, aging, or other durability conditions
• Whether the treatment is compatible with the final material and manufacturing process

Testing is therefore not simply a way to obtain a laboratory number. It can also be part of the product development and quality-control process.

2. What Should Be Tested?

The first step is to define what type of microbial protection is required.

Antibacterial Performance

Antibacterial testing evaluates the ability of a material or treatment to inhibit or reduce the growth of selected bacteria.

Depending on the application, manufacturers may select specific test organisms that are relevant to the intended use.

For textile products, for example, ISO 20743:2021 provides quantitative methods for determining antibacterial activity in antibacterial textile products, including nonwovens. The standard covers different inoculation approaches and measurement methods.

Anti-Mold and Antifungal Performance

If the primary concern is mold or fungal growth, antibacterial testing alone is not enough.

Mold protection should be evaluated using an appropriate fungal or mold test method and relevant test organisms.

This distinction is important because:

Antibacterial activity does not automatically demonstrate anti-mold performance.

A material may show strong activity against certain bacteria while requiring a different formulation or treatment approach for fungal protection.

Combined Antimicrobial Protection

Some applications require protection against both bacteria and fungi.

Examples may include:

• Textiles
• Plastics and polymers
• Rubber products
• Coatings and paints
• Silicone products
• Wood and bamboo products
• Leather and other moisture-sensitive materials

In these cases, the testing program should reflect the actual protection requirements rather than relying on only one microbial test.

3. Common Antimicrobial Testing Approaches

Different testing methods are designed for different materials and applications.

Quantitative Testing

Quantitative methods compare microbial populations between treated and untreated samples.

The result may be expressed as a reduction in viable microorganisms or another quantitative measure defined by the applicable test method.

This approach can be useful when manufacturers need to compare:

• Treated vs. untreated materials
• Different antimicrobial agents
• Different treatment concentrations
• Different application processes
• Initial performance vs. performance after durability testing

Qualitative Screening

Some test approaches are primarily used for screening or observing whether microbial growth is inhibited around or on a test material.

These methods can be useful during early-stage product development, but the result should be interpreted according to the specific method and material being tested.

A visible inhibition zone, for example, does not necessarily mean that the same antimicrobial behavior will occur in a finished product under real-world conditions.

Material-Specific Testing

The physical properties of the material can strongly influence the testing approach.

For example, ASTM E2180-24 is designed to quantitatively evaluate antimicrobial effectiveness in incorporated or bound antimicrobial agents on or in mainly flat polymeric or hydrophobic materials. It focuses primarily on antibacterial activity and can also accommodate other microorganisms such as yeast and fungal conidia under the method's scope.

This illustrates an important principle:

The test method should match the material and the way the antimicrobial agent is used.

4. Antibacterial Testing vs. Anti-Mold Testing

These two types of testing are related, but they are not interchangeable.

The selection should be based on the actual microbial risks associated with the product.

For example, if a textile manufacturer is mainly concerned about bacterial growth and odor, antibacterial testing may be appropriate.

If a product will be stored or transported under high humidity and the primary concern is visible mold growth, fungal or anti-mold evaluation becomes much more important.

5. What Factors Can Affect Test Results?

Antimicrobial test results do not depend only on the antimicrobial agent.

Several factors can influence the outcome.

5.1 Material Type

Textile fibers, plastics, rubber, coatings, wood, leather, and other materials have different surface structures and chemical properties.

These differences can affect how an antimicrobial agent is distributed, retained, or exposed on the material surface.

5.2 Antimicrobial Concentration

Using more antimicrobial agent does not necessarily mean that a finished product will always perform proportionally better.

The effective concentration depends on the antimicrobial chemistry, target microorganism, material, application method, and other formulation factors.

Testing different concentrations can therefore help identify an appropriate treatment range.

5.3 Application Method

An antimicrobial agent may be:

• Incorporated during polymer processing
• Applied by coating
• Applied through padding or exhaustion
• Added to a formulation
• Applied as a surface treatment

The same antimicrobial chemistry can produce different results depending on how it is introduced into the material.

5.4 Surface Properties

Antimicrobial activity often depends on the interaction between microorganisms and the treated material surface.

Surface roughness, hydrophobicity, porosity, coating structure, and other characteristics may affect microbial contact and recovery.

5.5 Washing and Aging

For products exposed to repeated washing, abrasion, heat, humidity, or long-term storage, initial antimicrobial activity may not tell the complete story.

Durability testing can help determine whether the treatment remains effective after the conditions expected during the product's service life.

ASTM E2180, for example, includes provisions that can be used to assess longer-term antimicrobial activity by comparing treated materials under different aging or washing conditions.

6. Why Can Two Laboratories Obtain Different Results?

It is possible for two tests to produce different results even when the same material and antimicrobial agent are used.

This does not automatically mean that one result is incorrect.

Differences can arise from:

• Test method
• Test organism
• Inoculum conditions
• Contact time
• Sample preparation
• Material characteristics
• Treatment concentration
• Recovery procedure
• Laboratory conditions

Therefore, antimicrobial results should always be interpreted together with the test method and test conditions.

A statement such as "99% antibacterial" is incomplete without knowing what was tested, how it was tested, and under what conditions the result was obtained.

7. How Should Manufacturers Interpret Antimicrobial Test Results?

When reviewing an antimicrobial test report, manufacturers should look beyond the final percentage or reduction value.

Important information includes:

Test Method

Identify the standard or method used for the evaluation.

Test Microorganisms

Check which microorganisms were tested.

The result applies to the organisms evaluated under the specified test conditions and should not automatically be generalized to all microorganisms.

Test Sample

Determine whether the test was performed on:

• Raw material
• Treated material
• Finished product
• Coated surface
• Polymer containing an antimicrobial additive

The test sample should represent the actual product as closely as practical.

Treatment Conditions

Review the antimicrobial concentration and application conditions.

A laboratory result obtained at one treatment level may not represent performance at another concentration.

Durability

If the final product will be washed, exposed to humidity, heated, or stored for long periods, durability testing may be necessary.

8. Laboratory Performance vs. Real-World Performance

A laboratory test is performed under controlled conditions.

Real-world environments are much more complicated.

A product may experience:

• Temperature changes
• High humidity
• Condensation
• Repeated washing
• Mechanical abrasion
• Chemical exposure
• Long-distance transportation
• Poor ventilation
• Organic contamination

For this reason, laboratory testing should be considered part of a broader product evaluation process.

For example, a textile treatment may show good antibacterial activity in laboratory testing, while the final product may still require appropriate moisture management and storage conditions to reduce the risk of mold during transportation.

Antimicrobial treatment is one part of material protection—not a replacement for proper processing, packaging, storage, or moisture control.

9. How to Select the Right Testing Strategy

A practical testing process can begin with five questions:

Step 1: What material are you protecting?

Identify whether the product is textile, plastic, rubber, coating, wood, leather, silicone, or another material.

Step 2: What microbial problem are you trying to control?

Is the main concern:

• Bacterial growth?
• Mold?
• Fungal growth?
• Odor associated with microbial activity?
• A combination of these problems?

Step 3: How is the antimicrobial agent applied?

Determine whether the antimicrobial agent is incorporated into the material or applied as a surface treatment.

Step 4: What conditions will the product experience?

Consider washing, humidity, heat, abrasion, storage, transportation, and expected service life.

Step 5: Which test method best represents the application?

Choose a recognized and appropriate test method based on the material, target microorganisms, and intended application.

The goal is not simply to select the most demanding test.

The goal is to select a test that meaningfully represents the performance requirement of the finished product.

10. Working With an Antimicrobial Agent Supplier

For manufacturers developing antimicrobial products, laboratory testing should ideally be connected with product formulation and application development.

A suitable antimicrobial solution may depend on:

• Material compatibility
• Target microorganisms
• Required dosage
• Processing temperature
• Application method
• Durability requirements
• Regulatory requirements
• Final product performance

For this reason, product selection should not be based only on a technical datasheet or a single laboratory result.

A more practical approach is:

Material → Microbial Risk → Antimicrobial Solution → Sample Trial → Performance Testing → Optimization

This process can help manufacturers identify whether a treatment is suitable for their specific material and production conditions.

11. Conclusion

Testing antimicrobial performance is an important step in developing and evaluating treated materials.

However, there is no universal antimicrobial test that can represent every material, microorganism, or application.

A reliable evaluation should consider:

• The material being protected
• The target microorganisms
• The antimicrobial technology
• The application method
• The treatment concentration
• The selected test method
• Durability requirements
• The intended end-use environment

For manufacturers, the most useful question is therefore not simply:

"Does this antimicrobial agent work?"

A better question is:

"Does this antimicrobial solution provide the required level of protection for my specific material and application?"

At Admire, antimicrobial and anti-mold solutions can be evaluated according to the material, application process, and microbial protection requirements. If you are developing a new product or experiencing mold or bacterial growth problems, providing information about your material, application method, target market, and microbial concern can help identify a more suitable treatment approach.

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If you are developing an antimicrobial product or evaluating different treatment options, our technical team can help you define a testing strategy based on your material and application.

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