by Daniel Mays Daniel Mays No Comments

ePTFE Sheet: Properties and Applications

Introduction

ePTFE sheet is a specialized material based on PTFE. While engineers have relied on PTFE for decades because of its chemical inertness, thermal stability, and ultra-low friction, PTFE does have its limitations. When a standard PTFE sheet is used in sealing applications with imperfect flange surfaces or inconsistent bolt loads, the material’s limited compressibility and tendency toward cold flow can lead to serious problems. 

Expanded PTFE (ePTFE), on the other hand,  addresses these challenges with its unique microstructure, and this microstructure gives it significantly better sealing performance while retaining the core benefits of PTFE. 

This blog post explains what ePTFE is, how it differs from conventional PTFE, and why it has become a preferred choice for gaskets and seals in harsh environments.

What is ePTFE?

ePTFE is a specialized form of PTFE that has been mechanically stretched under controlled heat and pressure. This engineered expansion introduces porosity and internal reinforcement into the microstructure of PTFE, transforming it from a dense, rigid sheet into a material that is highly compressible, conformable, and able to provide excellent long-term sealing performance.

How ePTFE Differs from Conventional PTFE

Both ePTFE and PTFE share the same chemical composition, but the expansion process dramatically changes the physical structure and performance of ePTFE. Here is a comparison.

Comparison of PTFE vs. ePTFE

AttributeConventional PTFEExpanded PTFE (ePTFE)
MicrostructureDense, non-porous solidPorous, fibrillated network created by expansion
Compressibility & ConformabilityLowHigh as it adapts to damaged or uneven flange surfaces
Creep/Cold FlowMore prone to cold flow under loadReduced creep due to the fibrillated structure
Sealability at Low Bolt LoadsModerateExcellent, as it reliably seals even when the bolt load is insufficient
DensityHighLower due to controlled porosity
BreathabilityImpermeableIt can be breathable depending on the expansion ratio and thickness

Because of the microstructure that results from the controlled stretching and heating, ePTFE is better suited for sealing imperfect flanges, systems with temperature cycling, or connections that are sensitive to bolt-load variations.

How ePTFE Was Developed

PTFE was discovered in the 1930s, and it was in the 1960s and 1970s when engineers began to experiment with mechanical expansion techniques. One such technique resulted in the fibrillated microstructure that gives ePTFE improved mechanical properties. Today, ePTFE is used everywhere from chemical plants and semiconductor lines to medical devices and filtration systems.

Material Properties of ePTFE Sheet

While ePTFE sheet does share some of the same properties as PTFE, there are some significant differences.

Mechanical Behavior

The fibrillated matrix of ePTFE provides it with higher compressibility and resilience. This means that it can conform to warped, scratched, or pitted flange surfaces while still retaining a reliable seal. Unlike standard PTFE, ePTFE experiences far less cold flow. This property improves its long-term stability under load.

Thermal Performance

ePTFE shares PTFE’s excellent resistance to extreme temperatures, and it handles thermal cycling exceptionally well. ePTFE’s structure reduces the stress concentration that can occur during expansion and contraction, which helps it to better maintain seal integrity.

Chemical Resistance

Like PTFE, ePTFE is nearly universally chemically inert. It resists aggressive chemicals such as strong acids, bases, solvents, oxidizers, and process chemicals. This makes it ideal for harsh chemical-processing environments.

Friction and Sealing Characteristics

ePTFE material retains PTFE’s extremely low coefficient of friction and non-stick surface. ePTFE also compresses easily and fills micro-voids at the interface, significantly improving leak-tightness even when gasket loads are low.

Microstructure

The microporous, interlocking fibrils combined to achieve an excellent balance of strength and flexibility. The amount of expansion determines other properties such as density, compressibility, and sealing capability. As a result, sheets can be engineered for specific applications.

Advantages of ePTFE Sheet Over Standard PTFE

ePTFE has several advantages over standard PTFE. For example, it exhibits better performance when working with flanges that have been damaged or are irregular. It also requires no fillers or reinforcements to achieve high performance. ePTFE has a higher level of recovery and compressibility when compared with PTFE, and also possesses improved creep resistance. It also has excellent sealing capabilities at low bolt torque. ePTFE is also known for its easy installation and rework

Design Considerations for Engineers Considering ePTFE

Engineers should consider the media, temperature, pressure, and chemical exposure associated with the potential application, keeping in mind that ePTFE performs well in the presence of aggressive chemicals and extreme temperatures. Additionally, ePTFE can better compensate for flange distortion, as well as scratches and pits. ePTFE sheets are available in both high and low density forms: high density sheets exhibit better mechanical stability, while lower density sheets have better compressibility. Selection of an ePTFE sheet depends primarily on the bolt lead, operating pressures, and flange quality. Finally, for standard gasket applications, non-venting ePTFE sheets are used as opposed to ePTFE membrane options.

Common Applications of ePTFE Sheet

ePTFE is used in a wide variety of applications, including the following:

  • Chemical Processing: Here, PTFE sheet is often used in pump housings, valve covers, manways, and flange connections that are exposed to corrosive media.
  • Semiconductor and High-Purity Environments: ePTFE has proven itself ideal for ultrapure chemical distribution where contamination must be minimized.
  • Food, Dairy, and Pharmaceutical: FDA-compatible ePTFE is used and is very resistant to media that includes CIP/SIP chemicals and steam, as well as repeated exposure to thermal cycling.
  • Oil and Gas: ePTFE gaskets withstand corrosive environments, fluctuating temperatures, and low bolt loads common in pipeline and processing equipment.
  • Medical and Life Sciences: ePTFE membranes serve as vents, filters, and barrier layers in medical devices.
  • General Industrial: This includes applications ranging from heat exchangers to compressors and agitators. In fact, HVAC systems frequently use ePTFE gaskets because of their sealing reliability.

Conclusion

ePTFE sheet is a significant improvement over conventional PTFE in sealing and gasketing applications. Its microporous structure delivers superior compressibility, conformability, and creep resistance while maintaining the outstanding chemical and thermal benefits of PTFE. Whether it’s used in chemical processing, food and pharmaceutical systems, semiconductor applications, or general industrial machinery, ePTFE offers reliable long-term performance. 

Advanced EMC is a supplier that offers a wide range of ePTFE sheets, tapes, and custom gasket solutions engineered for the most demanding service environments. Our expertise in polymer sealing allows Advanced EMC to assist you with material selection, thickness optimization, and application-specific sealing guidance. Contact us today to learn more.

Back-Up Rings
by Daniel Mays Daniel Mays No Comments

Choosing the Right Polymer Backup Ring

Choosing the right polymer backup ring can be challenging, but having a basic understanding of how they work, combined with some guidelines, can make the design decisions much easier. This blog post provides a brief overview of what backup rings are, what distinguishes polymer backup rings, and how to choose the right one for a specific application.

Backup Rings

Backup rings are supportive elements typically used with O-rings in sealing systems to help prevent extrusion in the clearance gap of a seal. Often used in high-temperature or high-pressure applications, these rings have lower coefficients of expansion and are engineered to be very rigid and tough. Backup rings can also help to evenly distribute pressure in applications involving varying clearance gaps or pressure fluctuations. Additionally, backup rings help to reduce the effects of wear and friction on O-rings and serve as a thermal barrier to protect them from excessive heat. 

Why Polymer Backup Rings?

Polymer backup rings are often used in place of elastomeric versions because they offer significantly better resistance to extrusion, deformation, chemical resistance, and long-term creep under high pressure. Materials like PTFE, PEEK, or Nylon tolerate wider temperature swings, aggressive fluids, and high-cycle dynamic motion without breaking down. The result is a more stable sealing system with significantly reduced risk of issues such as blowouts, spiral failure, or premature wear. 

Choosing the Right Polymer Backup Ring

There are several different factors that go into selecting the right polymer backup ring. 

Clearance Gap

The clearance gap is one of the most important factors when specifying a polymer backup ring. It directly determines how much support the O-ring needs to prevent extrusion. As the gap increases, the load on the elastomer rises, and the likelihood of extrusion rises sharply. This is especially true at higher pressures or temperatures.

Keep in mind that larger gaps typically require a stiffer polymer (such as PEEK instead of PTFE), a thicker or contoured backup ring profile, or even double backup rings for bidirectional pressure. Small, well-controlled gaps, however, may allow the use of thinner PTFE rings. In short, the wider the clearance gap, the stronger and more dimensionally stable the backup material must be..

Pressure and Temperature

Environmental factors that influence the selection of the right backup ring include system pressure, as higher pressures require harder, more extrusion-resistant materials. System temperatures, which impact dimensional stability, can limit the choice of materials based on their operating temperature limits. High temperatures can make materials more pliable, while low temperatures can lead to brittle behavior. Temperature also affects dimensional stability, as thermal expansion can increase the clearance gap and increase the likelihood of extrusion. 

Static or Dynamic

Another key factor in selecting a backup ring is whether the sealing system will operate in a dynamic or static environment. Static systems will involve less mechanical stress on the backup ring, allowing a wider range of polymer materials to be suitable. In contrast, dynamic applications that introduce continuous motion, friction, and side loading require tougher, more wear-resistant polymers with excellent dimensional stability, such as PEEK or certain PTFE blends. 

Backup Ring Shape

The two most commonly used backup ring shapes are the scarf-cut and solid types. Scarf-cut backup rings feature a single angled split that allows them to flex during installation. They can also conform more easily to the groove and reduce the risk of damage during assembly, since the ring can be expanded or compressed without overstressing the material. Because they can open slightly, scarf-cut rings are often chosen when hardware tolerances are tight or when installation must be done without special tools. 

Solid backup rings do not have a split and must be made from a more flexible polymer that allows them to be stretched or compressed into place without cracking. While they do not offer the same level of extrusion resistance as scarf-cut designs in extreme conditions, their continuous, unbroken profile provides uniform support and is useful in moderate-pressure systems where ease of installation and stable sealing performance are priorities.

Back-Up Ring Material

PTFE is an excellent option for backup rings due to its extremely low coefficient of friction and extensive chemical compatibility. Applications requiring dynamic sealing or very low temperatures are excellent opportunities to use PTFE. PTFE does have its limitations, however. There is the possibility of cold flow under sustained loads, which can make it unsuitable for extreme pressure conditions. Virgin PTFE is limited to about 3,600 psi. Filled PTFE (e.g., glass-filled, carbon-filled, graphite-filled, bronze-filled) is effective for pressures up to 5,800 psi.

PEEK possesses high mechanical strength and excellent resistance to extrusion, with thermal stability up to 480°F and exceptional resistance to extrusion. PEEK can be used at pressures up to 20,000 psi and a maximum temperature of 500°F. These properties make PEEK an excellent option for both high-pressure and high-temperature applications. Additional strength and hardness can be achieved by using various fillers. Finally, PEEK is compatible with a wide range of chemicals and exhibits very low friction. 

Nylon works very well in moderate conditions and is more economical compared to PEEK and PTFE. However, it does have some critical limitations that include swelling and water absorption, both of which can heavily impact tolerances. Nylon 6,6 works well at pressures below 10,000 psi and a maximum temperature of 186°F. Nylon 6,6 filled with Molybdenum Disulfide (MoS2) to reduce friction is commonly used for backup rings. However, one of the drawbacks of Nylon 6,6 is its water absorption, which can range from 0.5% to 1.4% per 24 hours.

Conclusion

Choosing the right polymer backup ring is ultimately about understanding the pressures, temperatures, clearances, and motion your system must withstand. When those variables are matched with the correct geometry and material, you will have a more reliable sealing system with fewer failures and a longer service life. If you need help evaluating your application or choosing the optimal backup ring design, Advanced EMC’s engineering team is ready to assist. Contact us today to discuss your requirements and get expert guidance on the best polymer sealing solution for your equipment.