ASTM D3111-19 Standard Practice provides a test method for determining the flexibility of hot-melt adhesives, evaluating their performance at specific temperatures through a mandrel bend test. This method is simple and fast, with low equipment investment and operator training requirements, and is suitable for testing whether hot-melt adhesives meet flexibility requirements. It can be used to compare the flexibility of different hot-melt adhesives, helping to design gluing agents that meet specific applications. However, this test method is mainly used for comparison and is not suitable for absolute characterization of gluing agents. Test results need to be performed at set temperature conditions to ensure accuracy.