The method of identifying the quality of FFKM is as follows:
1. Density: The density of FFKM material should be between 1.8-2.0 g/cm³. If the density is outside this range, it may be due to other substances being doped with the material.

2. Thermal stability: The thermal stability of FFKM material should be very high, and it can be used for a long time in a high-temperature environment without decomposition. The thermal stability of a material can be tested by detecting its thermal decomposition temperature or by performing tests at high temperatures.
3. Chemical inertness: FFKM materials should have excellent chemical inertness and be able to resist the erosion of various corrosive substances. The chemical inertness of a material can be tested by testing its resistance to various corrosive liquids.
4. Physical properties: FFKM material should have good physical properties, such as high elasticity, tear resistance, wear resistance, etc. The physical properties of materials can be tested by testing methods such as tensile tests, tear tests, and wear tests.

5. Product certification: FFKM materials usually need to go through ISO 9001 or ISO TS 16949 and other quality management certifications, which can be used as a reference for evaluating the quality of materials.