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Standard Method for Determining Resistance of Synthetic Polymeric Materials to Fungi

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ASTM G21 – Antifungal Resistance Test

ASTM G21 test method is used to determine the resistance of synthetic polymer and plastic materials to fungal growth.

Pure synthetic polymer materials are usually fungus resistant as they don’t act as a carbon source to support fungal 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.

ASTM G21 Test Requirements

  1. Fungus genus as test organisms
  2. The simplest specimens (with a size of 50×0-mm) and a rod or tube specimen (with a size of at least 76 mm)  are selected for testing.
  3. For film-forming materials (coatings), films with a size of 50×25 mm (2×1 in.) are selected for testing.
  4. If the specimen differs on two sides, then 3 specimens are needed to be tested having face up and face down surfaces.

Organisms typically used in this method: Aspergillus brasiliensis, Aureobasidium pullulans, Chaetomium globosum, Trichoderma virens, Penicillium funiculosum

ASTM G21 Test Method

  • Test specimens are placed on the solidified surface of nutrient salt agar and inoculated with spores suspension.
  • Inoculated test specimens are sealed properly and kept for incubation at 28 to 30°C under relative humidity conditions. In parallel, untreated test materials (control) are also inoculated and incubated.
  • The standard duration of incubation is 28 days. However, the test can be terminated earlier if test specimens display a growth rating of two or more.
  • After the incubation period, a rating scale between 0-4 determines the antifungal efficacy of tested materials. Ratings are described as below –

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 %)


Advantages of ASTM G21 Test Method

  • This single test method can be used to check the fungal resistance of materials against a  range of fungus species, collected from different environments.
  • For this test, standard conditions (growth medium, salts, minerals,  spore suspension, and humid environment) are designed in such a way that ensures the proper growth of fungus. Hence, ASTM G21 testing method evaluates the real efficacy of testing materials against fungal growth.

At Microbe Investigations (MIS), we test the efficacy of antifungal plastic finishes using ASTM G21 test and other standard test methods like AATCC-30.

With a team of experts and advanced technology capabilities, MIS provides a comprehensive suite of quality antiviral, antibacterial, and antifungal testing services worldwide.

Contact our experts here to know about pricing, turnaround times, and other related queries.


ASTM G21 is a qualitative test method that determines the efficacy of synthetic polymer materials against fungal growth.

ASTM G21 test can be used for a wide range of materials such as molded and fabricated articles, tubes, rods, coatings, pipes, marine plastics, sheets, and film materials.

The standard time duration of the ASTM G21 test is 4-6 weeks.

At Microbe Investigations, we test for the ASTM G21 using the fungal strains : Aspergillus niger (ATCC-16888). Additional strains can be added as per the customer’s testing requirements.

Contact us for more information

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