ePTFE vs CNAF: Which Gasket Material Should You Use?

You’re standing in front of a chemical processing line that needs new flange gaskets. One supplier quotes expanded PTFE, another recommends CNAF. Both claim their material is best for your application. So which one actually is?

The choice between ePTFE and CNAF gaskets isn’t just about price – it’s about matching material properties to your specific operating conditions. Select the wrong one, and you risk leaks, downtime, or premature failure.

Key Takeaways

• ePTFE excels in aggressive chemical environments and applications requiring FDA compliance, but costs more
• CNAF offers excellent value for general industrial use with oils, water, steam, and moderate chemicals
• ePTFE handles irregular flanges better due to superior conformability and lower bolt load requirements
• CNAF provides wider temperature tolerance (up to 400°C in some grades vs 260°C for ePTFE)
• Your operating conditions determine the right choice – chemical compatibility and temperature are the primary selection criteria

What is ePTFE?

Expanded PTFE (polytetrafluoroethylene) is created by stretching virgin PTFE under controlled conditions to create a highly porous, fibrous structure. This expansion process transforms solid PTFE into a soft, highly compressible material that maintains the chemical inertness of virgin PTFE whilst adding flexibility.

The microstructure consists of millions of microscopic fibres that allow the material to conform to surface irregularities whilst maintaining exceptional sealing performance. Unlike standard virgin PTFE sheet, which can be rigid and prone to cold flow, the expanded version offers superior recovery properties and dimensional stability.

Our expanded PTFE sheet is FDA-approved for direct food contact and pharmaceutical applications, making it the default choice for industries with stringent purity requirements.

What is CNAF?

Compressed Non-Asbestos Fibre gaskets are manufactured by compressing synthetic fibres (typically aramid, glass, or carbon) with a rubber binder under high temperature and pressure. The result is a dense, robust sheet material that replaced hazardous asbestos products following their ban in the 1990s.

The rubber binder is typically nitrile (NBR), although EPDM and SBR variants are also available, depending on the application. Different fibre compositions and binder combinations create various grades rated for specific temperature and pressure ranges. CNAF gasket sheet materials are available in grades ranging from general-purpose (BS7531 Grade Y) to high-performance specifications (BS7531 Grade X) for more demanding conditions.

For a deeper look at how CNAF compares to other options, see our guide on What is CNAF

Chemical Resistance Comparison

This is where ePTFE pulls decisively ahead. Expanded PTFE is chemically inert across the full pH range (0-14) and resists virtually all industrial chemicals except molten alkali metals and elemental fluorine at elevated temperatures. It won’t degrade when exposed to concentrated acids, strong bases, aggressive solvents, or oxidising agents.

CNAF gaskets offer good chemical resistance but aren’t universal. They handle oils, hydrocarbons, water, steam, dilute acids, and alkalis effectively. But expose them to concentrated acids or strong oxidisers, and the rubber binder becomes the weak point. The aramid fibres may resist chemical attack, but if the binder fails, the gasket loses integrity.

If your application involves pharmaceuticals, aggressive chemicals, or requires absolute purity, ePTFE is non-negotiable. For general industrial use with water, oils, or moderate chemicals, CNAF performs reliably at a fraction of the cost.

Temperature and Pressure Capabilities

CNAF gaskets typically handle temperatures from -200°C up to 300-400°C, depending on grade and specific formulation. Higher-grade CNAF materials with specialised binders and carbon fibre reinforcement can operate at the upper end of this range. Standard grades usually max out around 300°C.

Expanded PTFE operates effectively between -200°C and 260°C. While this upper limit is lower than that of high-grade CNAF, ePTFE maintains consistent performance across its entire temperature range without degradation.

Pressure capacity favours CNAF. These compressed fibre materials can handle pressures up to 140 bar in high-performance grades, making them suitable for demanding applications in power generation and heavy industry. ePTFE gaskets typically seal effectively up to 60-80 bar, although exact ratings depend on thickness and specific application details.

For extreme high-pressure and high-temperature combinations, particularly in oil, gas, and steam applications, consider alternatives like spiral wound gaskets, which offer superior pressure containment.

Conformability and Installation

Expanded PTFE’s soft, spongy structure is its key advantage here. The material compresses easily and conforms to rough, damaged, or irregular flange surfaces without requiring excessive bolt torque. This makes ePTFE ideal for glass-lined equipment, ceramic flanges, or older steel flanges with surface imperfections.

Lower bolt load requirements mean reduced risk of crushing delicate components or warping lightweight flanges. The material’s ability to fill surface irregularities creates reliable seals even on less-than-perfect sealing surfaces.

CNAF gaskets are firmer and require higher bolt loads to achieve proper compression. They work well on standard raised-face steel flanges in good condition, but struggle with irregular surfaces. If your flanges are damaged or you’re working with fragile equipment, the additional bolt load needed for CNAF could cause problems.

Both materials resist creep better than standard virgin PTFE, but ePTFE’s multidirectional fibre structure provides superior long-term load retention.

Cost and Availability

CNAF gaskets are significantly more affordable than ePTFE – often 40-60% less expensive for comparable thicknesses. The manufacturing process is simpler, and raw materials are less costly. For large-scale operations or applications where chemical inertness isn’t critical, CNAF’s cost advantage adds up quickly.

Expanded PTFE commands premium pricing due to its complex manufacturing process and the use of 100% virgin PTFE resin. But consider the total cost of ownership: if ePTFE’s superior performance prevents even one unplanned shutdown or product contamination incident, the price difference becomes irrelevant. Both materials are readily available in standard thicknesses and sheet sizes. Most gasket suppliers stock both options and can provide custom gaskets cut to your exact specifications.

When to Choose ePTFE

Select expanded PTFE gaskets when your application involves:

• Aggressive chemicals requiring universal chemical resistance
• Pharmaceutical or food processing with FDA compliance requirements
• Irregular, damaged, or delicate flange surfaces
• Equipment where bolt load must be minimised
• Applications requiring non-contaminating, chemically pure seals
• Corrosive services where gasket failure risks significant downtime

ePTFE is the safer choice when chemical compatibility is uncertain or when the cost of failure exceeds material cost considerations.

When to Choose CNAF

CNAF gaskets are the practical choice for:

• General industrial applications with water, oils, or steam
• Moderate chemical environments within the material’s compatibility range
• High-pressure systems (above 80 bar)
• High-temperature applications (above 260°C) using appropriate grades
• Budget-conscious projects where chemical demands are well-understood
• Standard steel flanges in good condition

Other Material Options to Consider

Don’t limit yourself to just these two options. Depending on your specific requirements, other materials might be more suitable:

Rubber gasket materials like nitrile, EPDM, or Viton offer excellent flexibility and compression for lower-temperature applications. They’re often the best choice for water systems, HVAC, and general sealing where extreme chemicals aren’t present.

For critical high-pressure applications, metallic gaskets or composite options may provide better long-term reliability. The right choice depends on your complete operating envelope – temperature, pressure, media, flange condition, and maintenance requirements all play a role.

Making Your Decision

Start by honestly assessing your operating conditions. If you’re dealing with aggressive chemicals or require absolute purity, ePTFE’s higher cost is justified. If you’re sealing water lines, oil systems, or moderate chemical processes, CNAF delivers reliable performance at better value.

Consider flange condition too. Older equipment with worn flanges benefits from ePTFE’s conformability. New equipment with precision-machined flanges works well with either material.

Browse our completed industrial gaskets to see application examples, or contact our team to discuss your specific requirements. We can recommend the optimal material based on your operating parameters and supply gaskets cut to your exact specifications.

The best gasket material is the one that matches your application’s demands whilst providing reliable, long-term sealing. Understanding the strengths and limitations of ePTFE and CNAF puts you in a position to make that choice confidently.