ASTM G21 is an industry standard that uses an intensive testing protocol for determining if fungi, including mold and mildew, can grow on a polymeric material. MAPEI uses a third-party lab and the ASTM G21 standard for testing the antifungal effectiveness of MAPEI products containing polymer that incorporate BioBlock technology. The ASTM G21 test uses a mix of mold and mildew spores that are commonly found in household environments. Product samples are placed on nutrient-containing plates and sprayed with a mixture of these fungi. For 28 days, the test plates are kept at a constant temperature of 84.2°F (29°C) and exposed to high humidity, which are excellent conditions for fungal growth. The samples are then examined for fungal growth. If no growth is present, the product is considered to not support mold/mildew/fungal growth.