# FKM elastomer

Specifying fluoroelastomer seals by polymer family, compound, cure, fluid exposure and qualified assembly performance.

Reviewed: 2026-11-01

Tags: materials, polymers, elastomers, fkm

FKM identifies a fluoroelastomer family, not a complete seal specification. The base polymer, compound formulation, cure system and finished geometry all matter. A purchase description such as “FKM, black, 75 Shore A” cannot alone establish fluid compatibility, low-temperature sealing or service life.

## Separate family, brand and compound

Parker's **V0747 FKM** gives **23% typical compression set after 70 h at 200°C** under **DIN ISO 815-1**, **25% deformation**, **specimen B, method A**. This is a laboratory recovery test. Check the actual fluid, squeeze, duty and allowable leakage for the seal. [Parker V0747 test table](https://test.parker.com/content/dam/Parker-com/Literature/Praedifa/Compound_Data_Sheets/EMG_PTD_Compound-Data-Sheet_FKM_V0747_EN.pdf)

Viton is Chemours' fluoroelastomer brand; its selection guide distinguishes multiple polymer families and grades. Its standard A, B and F families differ in monomer composition and fluorine content, with corresponding fluid-resistance differences. A brand name without the polymer type and compound identification still leaves material choices unresolved. The cited guide's actual footer is **C-11021 (9/19), ©2019**. [Chemours, Viton Selection Guide](https://www.chemours.com/en/-/media/files/viton/viton-selection-guide.pdf?rev=39ff73bce44549e0823e70d726799768)

Keep **FKM** and **FFKM** distinct. Trelleborg's chemical-compatibility guide has separate columns for FKM, specific Resifluor FKM products and Isolast FFKM. Those columns are not interchangeable. The guide is explicitly **Edition August 2012**, regardless of its recent web crawl date; use it as identified historical selection guidance and confirm current compound recommendations. [Trelleborg, Materials Chemical Compatibility Guide](https://www.trelleborg.com/medical/-/media/tss-media-repository/healthcare-and-medical/pdfs/mat_chem_comp_gb_en.pdf?rev=ff354787e7894034ba286a2ffc8e7e02)

## Cure and formulation affect the result

Chemours' technical overview explains that compounding variables substantially affect final vulcanizate properties. It distinguishes diamine, bisphenol and peroxide crosslinking systems and describes peroxide-cured specialty families. It notes enhanced resistance to particular aggressive oils, steam and acids for certain peroxide-cured polymers, while cautioning that other-fluid resistance is not generally changed merely by changing the cure system for the same polymer.

Consequently, “peroxide cured” is a useful requirement only within a specified material and application. It does not establish universal chemical superiority. Preserve the qualified formulation and manufacturing/cure requirements; changing the base polymer, additives or cure needs assessment against the finished-part requirements. [Chemours, Chemical Resistance of Viton overview](https://chemours-util.my.salesforce-sites.com/CRG_VitonOverview)

## A named compound example

Parker's **V0747, black FKM** sheet identifies **creator date March 3, 2022** and **print date March 29, 2023**. Selected typical results are:

| Test | Typical result | Test basis |
| --- | ---: | --- |
| Hardness | 75 Shore A | DIN ISO 48-4; specimen greater than 6 mm |
| Tensile strength | 13.5 N/mm² | DIN 53504; S2 specimen |
| Ultimate elongation | 190% | DIN 53504; S2 specimen |
| Compression set | 23% | 70 h at 200 °C; DIN ISO 815-1; 25% deformation; specimen B, method A |
| TR10 | −15 °C | ISO 2921; 2 mm specimen |

Parker expressly says its mean laboratory results are typical, are not specification values and may differ from finished-goods measurements. These tests do not qualify leakage or life. [Parker, V0747 Compound Data Sheet](https://test.parker.com/content/dam/Parker-com/Literature/Praedifa/Compound_Data_Sheets/EMG_PTD_Compound-Data-Sheet_FKM_V0747_EN.pdf)

Preserve every test condition when comparing compounds.

## Fluid compatibility is compound- and condition-specific

Chemours' overview gives a concrete example: in **methanol at 23 °C**, Viton A is rated **D because of volume swelling**, while Viton F, GFLT-S and Extreme ETP-S are rated **A**. This is a difference within a branded fluoroelastomer family, not a universal rating for everything supplied as FKM. Confirm the exact compound and full chemical mixture. [Chemours, methanol comparison](https://chemours-util.my.salesforce-sites.com/CRG_VitonOverview)

Chemours separately describes **Extreme ETP-600S** as a peroxide-cured specialty grade with resistance to specified polar fluids, strong bases, organic amines and high-pH fluids. Such a named specialty claim must not be copied into a general FKM compatibility list or assumed for an ordinary dipolymer seal. [Chemours, Properties of Viton](https://chemours-util.my.salesforce-sites.com/CRG_VitonProperties)

The manufacturer's chemical-resistance guide distinguishes **permeation**, bulk passage through defects or imperfections, and **degradation of material properties**. Low visible swelling therefore does not prove low gas permeation or establish a leak-tight assembly. Define the fluid's identity, concentration, additives, temperature, pressure, exposure duration and cleaning cycle alongside allowable property changes. [Chemours, chemical-compatibility selection guidance](https://www.viton.com/en/sales-support/chemical-resistance-guide)

Parker's V0747 sheet reports a **168-hour, 100 °C water/steam aging test** under DIN ISO 1817 with typical **+1 Shore A hardness change and +5% volume change**. This is an aging result at those conditions; it is not a general steam-service rating or proof of indefinite sealing under cycling pressure. [Parker, V0747 aging tests](https://test.parker.com/content/dam/Parker-com/Literature/Praedifa/Compound_Data_Sheets/EMG_PTD_Compound-Data-Sheet_FKM_V0747_EN.pdf)

## Temperature numbers need an application basis

Chemours distinguishes low-temperature flexibility measurements from brittle-point testing: brittle point concerns impact behavior and does not establish low-temperature sealing capability. Thus, a TR10 value, glass-transition result or generic temperature range must retain its original definition. Verify leakage and recovery in the intended gland, including cooling rate, squeeze, motion and fluid exposure. [Chemours, low-temperature test distinctions](https://www.chemours.com/en/-/media/files/viton/viton-selection-guide.pdf?rev=39ff73bce44549e0823e70d726799768)

## Qualification, handling and release

Qualify the seal and mating hardware together. Record gland geometry, squeeze and fill, clearances, surface finish, installation method, motion, pressure cycles, temperature cycles and allowable leakage. Define compression-set, swelling, hardness and retained-property criteria as needed, then verify the finished part under representative conditions.

Chemours warns that hazards can arise during compounding, processing, curing or high-temperature service and directs users to its handling precautions and ingredient suppliers' information. Raw polymer, curing chemicals and finished seals are different handling situations. Obtain current safety instructions for the actual materials and process; do not infer a safe processing temperature or disposal method from an end-use material chart. [Chemours, Selection Guide safety and handling](https://www.chemours.com/en/-/media/files/viton/viton-selection-guide.pdf?rev=39ff73bce44549e0823e70d726799768)

Retain compound and batch traceability through molding, cure, inspection and assembly. Separate typical data, contractual limits and qualified application results. Undated online guide pages are not assigned publication dates from crawl or copyright records, and no generic FKM pressure, temperature or lifetime guarantee is implied.

## Related reference

[Material selection through production](../grades-tempers-and-conditions.md)