Ensuring that tight seals are provided so no leaks occur and no contamination enters the application, correct o ring colour identification is essential.
These essential components are primarily used within water and gas distribution, the food and beverage sector, petrochemical applications, hydraulics, automotive, air conditioning, and aerospace, to name a few.
The o ring colour codes, which we will look at throughout this post, ensure that the o ring you choose is the most suitable for the environment to which it will be placed.
In addition, it is important to highlight that o ring colour is an aid to clear identification, however, it is not a guaranteed material standard, and conventions do vary between manufacturers.
Specialist Sealing Products supply a wide selection of o rings available to order directly online.
Alternatively, if you have a specific question, call us on 01535 274 776.
What does each o ring colour mean?
Different types of o rings may have different types of colour pigmentations to help users identify material type, cure system, and hardness grade.
In the table below, we outline the variations of o rings linked to properties and materials; however, note these listings are conventions and not guarantees.
| Colour | Common material(s) | Typical properties | Typical applications |
| Black | NBR, EPDM, neoprene, FKM, FFKM | Varies widely by compound; colour alone is not definitive | Most general sealing; confirm by datasheet |
| Green | HNBR (HSN), FKM | High temperature, fluctuating stress | Refrigeration, air conditioning |
| Brown / Red-brown | FKM (Viton) | High temperature, chemical resistance | Fuel, oil, chemical systems |
| Blue | Fluorosilicone, detectable compounds | Identification / detectability | Food, pharmaceutical (often metal detectable) |
| Yellow | HNBR / certified gas seals | Gas suitability where certified (EN 549) | Gas distribution (certified only) |
| Clear / translucent | Silicone, urethane | Inertness or abrasion resistance | Food contact, light duty |
Black o rings
The default colour for most materials, black o rings come in various material compounds such as FKM, NBR, Viton, Neoprene, for example, and these types of o rings are typically used in cooling systems.
Note: Before 1987, black was the only colour used by manufacturers to identify a specific o ring. However, as manufacturing changed and developed and new materials became available, different colourants were required to aid in the identification of the different materials in use.
Green o rings
Green o ring material is mostly manufactured with HNBR, FKM, and HNBR. Green o-rings are most suitable in applications where there is contact with water, or in the automotive sector, as they offer a high resistance to oil.
Brown o rings
Made of FKM and NBR, brown o rings are typically used within the petrochemical industry due to their high levels of resistance to varying chemicals and temperature ranges.
Blue o rings
Most often made from silicone compounds, blue o rings are identified due to their coloured cross section. Due to the nature of the material (high chemical and temperature resistance), these metal detectable o rings will typically be used in the food and beverage industry and the pharmaceutical sector.
Yellow o rings
Made of HNBR, PTFE, and in some cases EPDM, yellow o rings are often used within gas distribution applications, i.e., steam boilers, compressors, etc. These types of o rings, due to the nature of the applications where they are placed, must all be compliant with the standard EN 549.
Clear o rings
Transparent in colour, these types of silicone o rings are typically made up of silicone rubber or urethane. Offering high levels of abrasion resistance, this type of o ring is suitable for applications where only light duty from the o ring is required.
Note: The colour of an o ring does not solely identify the compound of the seal.
Green o rings vs black
The difference between two of the most common o rings, green and black, comes down to the makeup of their rubber material.
For example, black o rings are one of the most generic sealing solutions available, with carbon black added to rubber compounds such as NBR, EPDM, FKM, and Neoprene, as it offers higher UV and degradation protection.
Black o rings are also typically inexpensive and offer high levels of performance.
Alternatively, green o ring material can be HNBR or FKM, depending on the application the o ring is intended for (often more heavy-duty applications, as this material type can withstand high temperatures and fluctuating stress loads).
AC o rings
O rings for use within air conditioning units will typically make use of both black and green o ring types.
Typically, green o rings will be used within more modern automotive systems. Able to offer optimal performance in applications where temperatures can rise up to 150 degrees Celsius, as well as fluctuating pressures, these rubber compound o rings also provide a high-performance seal against oil.
Black o rings are a standard o ring that are suitable for older AC systems, offering a good low-temperature sealing solution.
Each o ring material offers various properties, making them suitable for different applications and processes. It is important to opt for the most suitable material to provide the best seal for your application.
Limits of identifying o rings by colour
As previously highlighted, the colours mentioned are typical conventions but not guarantees, and as manufacturers vary, custom colours will and do exist.
Limitations of identifying o rings by colour include:
- There is no universal standard, so basing solely on colour can be incredibly unreliable
- Manufacturers can use custom colours
- The same colour can represent different materials
- Hardness can still vary by manufacturer, not just identified by colour
- Not basing the decision on actual technical compound information can prove detrimental.
The only reliable method of choosing the right o ring for your application is to confirm the material against a datasheet.
(Note: Certified water seals (EN 681-1) and gas seals (EN 549) are a separate and regulated colour system.)
FAQ
Q: What is the difference between green and black o rings?
A: The main difference primarily lies in the makeup of the rubber compound. In essence, black o rings are cost-effective and used for standard applications and general sealing. Alternatively, green o rings offer slightly higher levels of chemical and temperature resistance.
Q: What colour are AC o rings?
A: In modern automotive AC applications, green is the most commonly used o ring. However, in older AC applications, black o rings will provide a suitable seal.
Q: Are o ring colours standardised?
A: No, there is currently no standardisation of o rings colours, and these can vary from manufacturer to manufacturer. This is why we always recommend referring to the correct datasheet to ensure the most suitable o ring type.
Q: What colour is a Viton ring?
A: Viton o rings are typically brown in colour and offer high temperature and chemical resistance, making them suitable for fuel, oil, and chemical applications.
Q: How do I confirm an o ring material for certain?
A: We recommend always referring to the datasheet provided, which should outline the certificate of conformance, hardness measurement, temperature range suitability, specific gravity test, and more.
For further information on how to identify o ring materials, speak to one of our specialists today.
Call 01535 274 776 or visit our stock pages online to find out more. Click the button below.
