ASTM D751 - Blocking Resistance
Blocking at elevated temperatures (510°F) in a standardized oven is a test used in NFPA 1975 to evaluate for melting and sticking. A material is placed between two glass plates and into the oven at 510°F for 6 hours. Specimens are allowed to cool one hour before evaluation and are then checked for melting, sticking and evidence of ignition. The rating of resistance to blocking is also assigned using the ASTM D751 standard.