When sourcing PTFE mechanical seals, you must prioritize material purity and filler types. Pure PTFE is excellent for chemical resistance, but for mechanical strength, look for glass fiber, carbon, or graphite-filled PTFE to improve wear resistance. Ensure the operating pressure (typically up to 25 bar) and temperature range (-180°C to +260°C) align with your machinery's requirements. Additionally, verify the surface roughness (Ra) of the seal face, which should ideally be below 0.4 μm to prevent leakage.