How to read O-ring chemical compatibility ratings
Selecting the right seal material starts with knowing how the elastomer will behave when it contacts your process fluid. This chemical compatibility chart rates each common O-ring material — Nitrile (NBR), Hydrogenated Nitrile (HNBR), Fluorocarbon (FKM/Viton), Perfluoroelastomer (FFKM/Kalrez), EPDM, Silicone (VMQ), Neoprene (CR) and others — against dozens of industrial chemicals, fuels, acids, bases and solvents.
The ratings follow a simple A–D scale. A (Excellent) means the material shows little or no change after exposure and is well suited to the fluid. B (Good) indicates minor swelling or property change that is usually acceptable. C (Fair) warns of moderate volume swell, hardness change or strength loss — usable in some static, low-duty situations but worth testing first. D (Not Recommended) signals severe attack: excessive swell, embrittlement or dissolution that will likely cause leakage or failure. An X simply means there is not enough published data to give a confident rating, so treat the pairing as unknown until verified.
The ambient-condition caveat
Every value here is representative at ambient conditions (roughly 20°C, atmospheric pressure, dilute or standard concentration). Compatibility is not a fixed property — it shifts with temperature, chemical concentration, system pressure and how long the seal stays wetted. A material rated A at room temperature can drop to C or D in hot, concentrated or pressurised service. Cyclic exposure, mixtures and trace contaminants further complicate things. Use this chart to shortlist candidate materials quickly, then confirm the final selection against your real duty cycle — or send us your conditions and our engineers will recommend a compound.