PTFE O-rings: Universally resistant across the widest temperature range

What are PTFE O-rings?

PTFE O-rings are made from solid polytetrafluoroethylene, a semi-crystalline fluoroplastic. It is the same material that became known under the brand name Teflon.

Here’s how to interpret the diagram: The gray chain of carbon atoms (C) forms the backbone of the polymer. Fluorine atoms (F) are attached to each carbon atom at the top and bottom. The green frame represents the seamless protective fluorine shell: The fluorine atoms completely envelop the carbon chain and shield it from the outside.

That is exactly what makes PTFE so stable. The bond between carbon and fluorine is one of the strongest single bonds in organic chemistry. Because the chain is completely surrounded by fluorine, attacking substances find no point of attachment, unlike in materials with exposed hydrogen atoms.

In practice, this means that PTFE is chemically resistant to virtually everything—including acids, alkalis, solvents, and superheated steam—across a very wide temperature range. The trade-off is a lack of rubber-like elasticity. PTFE is a thermoplastic and is prone to cold flow, which is why it is primarily used as a flange gasket or as a jacketed O-ring.

Unlike elastomers, PTFE is a thermoplastic and therefore not rubber-like in its elasticity. The ring is made entirely of a single material, with no core or jacket. This makes it extremely chemically resistant, but it lacks the resilience of rubber.

Key Features

• Nearly universal chemical resistance: resistant to virtually all acids, alkalis, and solvents. Check specific chemicals using the Chemical Resistance Tool.
• Wideest temperature range: −250 to +250 °C, the widest of any sealing material.
• Very low friction: excellent non-stick and gliding properties.
• Non-elastic: thermoplastic, without rubber-like recovery.
• Hardness: 60 Shore D; PTFE is measured on the harder Shore D scale.
• Approvals: FDA. Shelf life: virtually unlimited.

PTFE is the material of choice when chemical resistance and an extreme temperature range are important, and a static flange seal is sufficient.

Comparison of Temperature Ranges

No other sealing material covers such a wide temperature range as PTFE: from −250 to +250 °C. For cryogenic applications, PTFE is therefore often the only choice. The graph shows how PTFE compares to other materials.

Continuous operating temperatures for typical sealing materials in standard formulations; NH materials in "Koralle" formulation. Values are approximate and depend on the formulation; refer to the respective data sheet for specific details.

Price Levels in Comparison

PTFE falls within the mid-range price bracket, being less expensive than FEP-coated materials and significantly cheaper than FFKM. The graph shows the relative price levels, with NBR—the least expensive option—set as the baseline (1).

Cost per material is provided as a guideline, with NBR set as the baseline (1) and NH high-performance materials shown in coral. These values are intended as a rough guide. The actual price depends on dimensions, formulation, and quantity.

What is PTFE resistant to?

PTFE is one of the most chemically resistant materials in existence. It is fully fluorinated and inert to nearly all substances:

• Acids and alkalis, including concentrated ones
• Solvents, ketones, and esters
• Oils, Fats, and Fuels
• oxidizing and corrosive substances

Very few media attack PTFE—such as elemental fluorine and molten alkali metals—similar to FFKM.

Characteristics: Cold flow and lack of elasticity

Two properties fundamentally distinguish PTFE from elastomers:

Lack of elasticity: PTFE does not spring back. The sealing effect is achieved through deformation during tightening, not through elastic preload as with rubber.

Cold flow: Under sustained pressure, PTFE deforms slowly and permanently (creep, also known as cold flow). The design must take this into account, for example by limiting the compression and using a closed groove.

A Comparison of PTFE, FEP, and FFKM

Three materials offer nearly universal resistance, but differ in elasticity, temperature, and price:

PTFE excels in terms of temperature range and durability; FEP adds a springy core; FFKM offers full elasticity.

Technical Specifications at a Glance

The following values are taken from the PTFE data sheet and have been tested in accordance with ASTM.

Shore D hardness per ASTM D2240, tear strength and elongation at break per ASTM D412, density per ASTM D1817. Compression set and TR-10 are not meaningful for PTFE as they are for elastomers and are provided upon request. The data sheet is authoritative.

Installation and Design

PTFE O-rings are not elastic and are used exclusively as static flange seals:

• Installation in a closed groove; not for use as a piston or rod seal.
• The ring cannot be stretched over components. The groove must allow the ring to be inserted without stretching; it is often designed as a split or open groove.
• Limit the compaction to keep cold flow to a minimum.
• You can determine groove dimensions and tolerances using the O-ring groove calculation and O-ring tolerances.

Typical applications

Are there alternatives to PTFE?

If the seal requires elasticity or a dynamic function, PTFE is not suitable. In that case, FFKM (ECOLAST) is the right choice for full elasticity, or FEP-coated O-rings for a springy core. If the application involves only oils and fuels in the mid-temperature range, FKM is the most cost-effective solution.

Frequently Asked Questions