O-ring material labels such as NBR, EPDM, FKM and HNBR identify broad elastomer families, not one universal compound. Parker’s handbook compares common families with qualitative ratings for properties including oil resistance, cold performance and tensile strength. The table below keeps a selected set of those ratings together so you can narrow a material question before opening the exact supplier datasheet. It is a screening reference: the working fluid, temperature, pressure, movement and compound formulation determine whether a specific seal is suitable.

O Ring Elastomer Material Properties

The letters are Parker’s qualitative scale: P means poor, F fair, G good and E excellent. Combined labels such as FG or GE are retained as printed combined ratings; they are not numeric scores and should not be ranked as if they were measured test results. The Parker compound prefix helps locate products in that manufacturer’s catalog. Another supplier may use different compound codes for the same polymer family.

How to read the comparison

Start with the property that can eliminate a candidate. If a seal contacts petroleum oil, NBR is often a candidate to investigate, and Parker rates its oil resistance above many other broad families. EPDM can be appropriate for water and weather exposure but is generally not the material to select for petroleum oil. FKM is known for broad chemical and heat capability, while low-temperature flexibility and dynamic behavior may become limiting. HNBR offers a different balance of heat, wear and oil properties. These are starting points, not universal pass/fail rules.

Each column describes a different material behavior. “Cold resistance” is not the same as a guaranteed minimum service temperature, and “heat resistance” in a qualitative table does not establish a continuous operating limit. “Tensile strength” is a broad family-level comparison; it does not provide a compound’s measured strength, hardness or elongation. “Set resistance” concerns recovery after compression, but it cannot predict leakage without knowing squeeze, groove fill, temperature and aging.

Use it as a screening step

For a hydraulic cylinder exposed to petroleum-based fluid, a designer might compare NBR and HNBR, then check each exact compound’s compatibility, hardness and temperature limits. If the assembly moves continuously, dynamic wear and lubrication matter. If the seal sits outdoors, ozone and weather resistance deserve attention. If the application uses hot water or steam, compare the specific compound’s steam compatibility rather than inferring performance from a general polymer label.

Record the exact manufacturer, compound designation, hardness, fluid, operating temperature range, pressure, motion type and expected service interval. Where several media contact the seal, evaluate the combined exposure. A compound that performs well in one fluid can swell, soften or lose resilience in another. Cleaning agents, additives and process contaminants can change the result.

Limits before specification

The handbook table is a broad comparison across polymer families. It does not establish a pressure rating, food-contact approval, potable-water compliance, aerospace qualification or compatibility with a named chemical at a particular concentration. Do not select an O-ring from one favorable letter alone, and do not treat the prefix as a complete part number. Confirm the exact compound datasheet and the seal manufacturer’s current compatibility information before releasing a drawing or maintenance substitution.

Gland dimensions are a separate design question. A compatible material can still fail if squeeze, stretch, extrusion gap, finish or installation damage is wrong. Conversely, the correct groove geometry cannot compensate for an incompatible elastomer. Use the material comparison to narrow the search, then complete the compound and gland checks for the actual assembly.

Sources

Property ratings are selected from Parker Hannifin’s O-Ring Handbook, ORD 5700, Table 2-2. Parker describes these comparisons as general elastomer properties and discusses compound and application conditions elsewhere in the handbook. Consult the current compound-specific documentation before design or replacement.