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ASTM G21 Fungal Resistance Testing for Polymeric Materials
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Summary
ASTM G21 testing is performed to evaluate the resistance of synthetic polymeric materials to fungal growth under controlled laboratory conditions. Materials susceptibility to mold contamination is rated on a scale from 0 (no growth) to 4 (heavy growth). Manufacturers use ASTM G21 test results to validate antifungal performance and durability claims.
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Quick understanding of the test
ASTM G21 - Fungal Resistance Test
- Aspergillus brasiliensis
- Talaromyces pinophilus
- Chaetomium globosum
- Trichoderma virens
- Aureobasidium pullulans
- Test specimens and controls are placed on nutrient-salt agar and are inoculated with spore suspension.
- Samples are incubated at specified temperatures for up to 28 days.
- Specimens are rated on a 0โ4 scale based on fungal coverage.
- Helps manufacturers to improve material formulations for better antifungal efficacy.
- Assists in meeting industry and safety standards for antifungal properties.
Turnaround Time
Passing criteria
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What is ASTM G21 testing?
ASTM G21 is an international standard that describes the test method for determining the resistance of plastics and polymers to fungal growth. In general, synthetic polymers are resistant to the growth of fungi as they do not provide the nutrients required for their growth.
However, other components or additives (such as plasticizers, lubricants, stabilizers, cellulose, and colorants) used in the making of synthetic plastic materials trigger the fungal growth and deterioration process. Therefore, antifungal resistance tests are important to ensure the durability and lifespan of plastic materials that can be affected by fungal growth.
What Does ASTM G21 Measure?
ASTM G21 primarily measures visible fungal colonization on polymeric materials under favorable conditions, typically:
- Temperature: 2โ38ยฐC (35โ100ยฐF)
- Relative humidity: 60โ100%
ASTM G21 simulates conditions to ensure how well a material resists mold and fungal growth in real-world environments.
Materials Tested under ASTM G21
ASTM G21 test method can be used to check the antifungal performance of the following materials –
- molded and fabricated articles,
- tubes,
- rods,
- coatings,
- pipes,
- marine plastics
- sheets,
- and film materials
Fungal Strains used in ASTM G21
- Aspergillus brasiliensis
- Aureobasidium pullulans
- Chaetomium globosum
- Trichoderma virens
- Penicillium funiculosum
ASTM G21 Test Method Explained
1. Preparation and inoculation
- The test specimens are placed on the solidified surface of nutrient-salts agar and inoculated with a spore suspension. This setup mimics real-world conditions where fungi encounter the materials in a nutrient-rich environment.
- Untreated control samples are also inoculated and incubated alongside the test specimens to provide a baseline for comparison.
2. Incubation
- The inoculated samples are then sealed and incubated at a temperature range of 28ยฐC to 30ยฐC, and under conditions of 90% relative humidity.
- The standard incubation period is 28 days but the test may be terminated earlier if the test specimens show considerable mycelial growth, usually indicated by a growth rating of two or more.
ASTM G21 Rating Scale and Interpretation
Evaluation and rating – After the incubation period, the samples are rated on a scale of 0-4 as mentioned below:
Rating Scale | Description |
0 | No growth on the specimen |
1 | Traces of growth on the specimen (less than 10 %) |
2 | Light growth (10 to 30 %) |
3 | Medium growth (30 to 60 %) |
4 | Specimens completely covered with growth (60 %) |
ASTM G21 vs Other Standards
Criterion | ASTM G21 | ISO 846 | ASTM E2180 |
Purpose | To assess antifungal resistance of plastics and polymeric materials | To assess microbial (fungal & bacterial) deterioration of plastics | To evaluate the antimicrobial activity of hydrophobic or polymeric surfaces under moist conditions |
Test microorganisms | Aspergillus brasiliensis, Penicillium funiculosum, Chaetomium globosum, Trichoderma virens, Aureobasidium pullulans | Aspergillus brasiliensis, Penicillium funiculosum, Paecilomyces variotii, Chaetomium globosum, Trichoderma virens | Staphylococcus aureus (ATCC 6538P), Pseudomonas aeruginosa (ATCC 15442) or Klebsiella pneumoniae (ATCC 4352) |
Scope of products | Synthetic polymeric materials (films, sheets, molded parts) | Plastics with even, cleanable surfaces (includes solid plastics; excludes porous foams) | Antimicrobial-treated polymeric materials (Medical devices, Shower curtains, etc) |
Result interpretation | Qualitative: Visual fungal growth rating (0โ4 scale) | Qualitative: Visual assessment of deterioration vs controls | Quantitative: Reduction in bacterial colonies compared to untreated controls |
Benefits of ASTM G21 Testing
Fungal Resistance Assessment
Determines how well a material resists mold and fungal growth.
Durability Insight
Helps predict long-term performance in humid or damp environments.
Supporting innovation and development
By assessing how additives and formulations influence fungal resistance, the test supports R&D efforts to create durable materials with improved antifungal efficacy.
Versatility in application
This test is applicable to a wide range of materials and products. From coatings and films right through to tubes, rods and fabricated articles, the test can be applied to various types of synthetic polymers and plastics.
Aids Regulatory and Market Acceptance
Meeting ASTM G21 requirements strengthens credibility and supports regulatory submissions or international trade approvals.
Strengths of ASTM G21 test method
- ASTM G21 uses multiple fungal strains from diverse environments, each with different nutrient and enzyme requirements. This ensures a thorough assessment of the materialโs antifungal performance.
- The ASTM G21 test uses a high spore concentration, which gives materials a tough and consistent fungal challenge to check how well they can withstand growth and damage.
- The test simulates real environmental conditions, providing a realistic measure of how materials perform in humid, marine, or construction settings prone to fungal exposure.
Limitations of ASTM G21 test method
- If the spore mixture isnโt prepared properly or contains leftover nutrients, it can encourage abnormal fungal growth and give misleading results.
- The results are based on visual scoring, which can vary between technicians.
- The 28-day incubation period can be quite long for manufacturers who need rapid screening or quick go-to-market decisions.
Why choose our lab
MIS Lab provides ASTM G21 testing to ensure your materials stand up to fungal challenges.
- Ensure your synthetic polymers resist fungal growth.
- Validate your productโs antifungal performance with precision.
- Our lab delivers reliable, standardized ASTM G21 testing.
- Get actionable results to strengthen your product claims.
- Partner with us today for trusted antifungal testing.
Get a quote for ASTM G21
Contact our experts here to learn about the pricing, turnaround times and other related queries.
Frequently Asked Questions
DR. Martinoz Scholtz
ASTM G21 assesses the resistance of synthetic polymers to fungal growth, typically reported as a visual mold rating on the specimen. While, ISO 846 evaluates the biodeterioration of plastics by microorganisms. It covers both fungi and bacteria, assessing growth, inhibition, and any resulting effects on the material.
ASTM G21 testing typically takes 4-5 weeks
Materials fail ASTM G21 when they show moderate to heavy visible fungal growth, usually falling under a visual rating of 2 or higher, indicating insufficient resistance to fungal growth.
While ASTM G21 is not mandatory for antimicrobial plastics, it is widely used to support antifungal or fungal-resistance claims required by consumers.
Yes, ASTM G21 can be applied to coatings, surface-treated materials, and polymer films.
ASTM G21 is commonly required in construction, healthcare, electrical, consumer goods and packaging industries, where materials are expected to resist fungal growth in humid environments.
For passing criteria , this standard uses a rating scale of 0 to 4. 0 indicates no growth (highly resistant), and 4 indicates extensive growth (very low resistance).
ASTM G21 is not required, but it is commonly used as accepted scientific evidence to substantiate antifungal or fungus-resistant claims for plastic materials.
A rating of 0 (no growth) or 1 (trace growth) is considered a pass in ASTM G21 testing.
ASTM G21 can assess fungal resistance of biodegradable plastics, but it does not measure biodegradation or compostability, which require separate biodegradation standards.
Yes. ASTM G21 is widely accepted in international markets as a recognized method for evaluating fungal resistance of plastics and polymeric materials.
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