What Do O‑Ring Colours Mean?

O-rings are circular cross-section sealing rings. They are a type of technical seal designed to maintain tightness between machine parts, equipment, and their components. O-ring seals are made from various rubber and silicone compounds with unique formulations, which give them specific properties and advantages.

Types of O-Ring Materials

EPDM O-rings offer high elasticity, resistance to deformation and abrasion. Under mechanical pressure, they retain their structure and return to their original shape after compression. They are widely used in many industrial sectors, such as the automotive industry. They perform well in contact with glycol- and silicone-based brake fluids. EPDM rubber seals are resistant to steam, ozone, mild acids, and hot water.

NBR O-rings have good mechanical properties (abrasion and deformation resistance). They are widely used due to their compatibility with petroleum-based products and applications involving elevated temperatures. Their working temperature range is from -30°C to +110°C.

Silicone O-rings (VMQ) are also known as high-temperature seals. They are resistant to both low and extremely high temperatures. Their main advantage is biological inertness. They do not absorb tastes or odours. VMQ O-rings are FDA-approved for contact with food and drinking water. They are ideal for use in medical, pharmaceutical, food processing and catering industries.

FKM O-rings are usually made from high-quality fluorocarbon rubber. They are also known as oil-resistant o-rings because of their excellent resistance to oils and greases. They offer low gas permeability and perform well in environments exposed to sunlight, high temperatures, and harsh weather. They are resistant to deformation and thermal ageing.

PTFE O-rings (Teflon) are available in various colours. They are made from one of the most chemically resistant materials. These are static seals with high rigidity. They are resistant to high temperatures, moisture, and UV radiation. PTFE o-rings are used in the petrochemical, chemical, and pharmaceutical industries.

O-rings have a wide range of applications in the automotive, food, medical, pharmaceutical, aerospace and home appliance industries.

O-Ring Colours

Let's take a look at what O-ring colours mean.
The colour of an o-ring is the result of technological development and smart use of material knowledge. Modern technologies allow for the production of o-rings in virtually any colour (e.g. purple HNBR o-rings resistant to diesel fuel). Although colours are arbitrary, some standards have been widely adopted worldwide.

Black O-rings

This is the most common o-ring colour. Black o-rings can be manufactured from a wide range of elastomer materials. In this colour, you can find seals made from the most popular and cost-effective NBR. FKM/FPM/Viton® rubber rings are also available in black. O-rings used in cooling systems – for contact with Freon® – made from Neoprene (resistant to oils, ozone, UV, ageing and weather) also come in black, as do VMQ (silicone) rings. Black EPDM rubber seals are recommended for use in applications exposed to sunlight.

Red O-rings

Red o-rings are made from silicone.

Brick-Coloured O-rings

These slightly lighter o-rings are made from VMQ silicone. They are often used in the food and medical industries because they are FDA-approved for contact with food and drinking water.

Green O-rings

Green o-rings are most commonly made from EPDM, recommended for water contact, as well as from FKM/Viton®. For applications requiring high resistance to oil and abrasion, such as systems that are frequently dismantled, HNBR seals – typically produced in green – are recommended.

White O-rings

PTFE o-rings – rigid and most often white. They are also produced in other colours. Similarly, VMQ/MVQ rings can be found in both white and other colours without altering their sealing properties.

Silver O-rings

Silver o-rings are usually made from fluorocarbon blends like FKM/FPM/Viton®.

Blue O-rings

O-rings in blue are typically made from silicone or FKM blends, which offer higher chemical resistance and a wider temperature range than standard NBR o-rings.

Brown O-rings

In this colour, you’ll find Viton® OP rings and those made from synthetic rubber such as NBR.

Graphite O-rings

Usually made from FFKM (used in aerospace applications) or FPM, which are recommended for contact with mineral oils.

Orange O-rings

Orange o-rings are usually produced from silicone (MVQ).

Transparent O-rings

MVQ silicone can also be produced in transparent form.

Yellow O-rings

Yellow o-rings are typically made from silicone, PTFE or EPDM (used in steam boilers, compressors and ozone-exposed environments).

Purple O-rings

These seals are made from EPDM or MVQ and are often used in food processing applications involving liquids.

Milky O-rings

Milky-white o-rings are fairly common. Depending on their application, two main variants exist:

1. For food contact: silicone compounds marked VQM or MVQ, also used in high-temperature environments up to 260°C, and up to 300°C in high-temp grades.

2. Advanced: made from FFKM (Kalrez® by DuPont®), specifically developed for contact with food.

Skin-Coloured O-rings

These are specialised compounds made from FFKM, officially known as Kalrez®. The light brown, skin-tone colouring is intended for pharmaceutical use. The key factor for using these o-rings is their exceptional resistance to aggressive chemicals, though this comes with a higher price.

Grey O-rings

In Poland, the grey colour is typically associated with OP sealing rings. These are usually made from FKM/FPM and are recommended for use with mineral and synthetic oils. They are used in passenger, racing, and heavy-duty engines, as well as military vehicles. Grey NBR compounds are also available, providing a cost-effective option.

Matte O-rings

As mentioned earlier, o-ring colour may indicate the material. The compounds used for sealing rings have various properties that make them suitable for specific working conditions and applications. Matte o-rings do not have a shiny finish. Their surface diffuses light and is free from gloss and reflections. Note that neither the colour nor the finish (matte or glossy) affects the function or performance of the seal. It is purely a visual attribute that may help identify the type of seal, the material, or even its hardness.

Glossy O-rings

The more light an o-ring reflects, the shinier it appears. A glossy surface makes the o-ring’s colour seem more vibrant. Glossy o-rings reflect most of the light falling on them. This type of finish is useful if the seal needs to be more noticeable. Colour coding helps distinguish materials according to industry standards.

O-Rings – Colour Guide Summary

The POWER Rubber team of rubber specialists has shared expert knowledge about technical seals. In this article, we explained what o-ring colours mean, listed the most common colours, explained their meanings and applications, and described the typical compounds used in production.

Coloured O-Ring Production – Direct from the Manufacturer

If you require o-rings in custom colours or specific sizes, feel free to contact our team of specialists.