PTFE Envelope gaskets

What Are PTFE Envelope Gaskets?

A PTFE envelope gasket is a composite gasket consisting of a PTFE outer envelope with an internal insert (inlay)
The PTFE layer provides excellent chemical resistance, while the core material adds strength and recovery, combining the benefits of multiple materials into a single sealing solution
These gaskets are typically used as flange gaskets in applications requiring high chemical resistance and sealing reliability

Key Benefits of PTFE Envelope Gaskets

Outstanding chemical resistance – PTFE is resistant to most corrosive media, vapours and fluids
Wide temperature capability – suitable for both low and high temperature environments
Non-contaminating – ideal for food, pharmaceutical and hygienic processes
Excellent sealing performance – reduces leakage in aggressive or sensitive systems
Non-stick surface – prevents material build-up and eases removal
Durable and long-lasting – resistant to ageing, weathering and degradation

PTFE envelope gaskets are widely used because they combine chemical inertness with mechanical strength from the insert material

Typical Applications

PTFE envelope gaskets are used across multiple industries where standard gasket materials may fail:

Chemical processing and petrochemical plants
Pharmaceutical and food processing systems
Water treatment and utilities
Oil and gas operations
Power generation facilities
Glass-lined and enamelled equipment
Pumps, valves and pipeline flange connections

They are especially effective in corrosive environments or where product contamination must be avoided

Types of PTFE Envelope Gaskets

Different envelope styles are available depending on pressure, media and application:
U-Type Envelope

Suitable for medium to high pressures
Most commonly used configuration

Double U-Type

Enhanced sealing for higher pressures
Additional protection where media exposure is critical

C-Type Envelope

Suitable for flexible insert materials
Used where adaptability is required

V-Type / Slit Envelope

Cost-effective solution for lower pressure applications

Donut / Fully Encapsulated

Used where media contact on all surfaces must be prevented

Envelope selection depends on flange design, pressure and sealing requirements.

Inlay (Insert) Materials

The internal core of a PTFE envelope gasket can be tailored to suit performance needs:

Compressed fibre (CNAF)
Rubber (EPDM, NBR, etc.)
Graphite
ePTFE
Corrugated metal inserts (for higher pressure applications)

The insert provides mechanical strength and resilience, while the PTFE envelope protects against chemical attack

When to Use PTFE Envelope Gaskets

PTFE envelope gaskets are ideal when:

The media is highly corrosive or aggressive
Cleanliness or hygiene is critical
Standard gasket materials degrade or contaminate
Flanges include glass-lined, plastic or coated surfaces
A combination of chemical resistance and mechanical strength is required

They are commonly selected where traditional rubber or fibre gaskets cannot provide sufficient resistance or longevity.

Custom PTFE Envelope Gaskets

Ashton Seals can supply:

Standard flange sizes (DIN, ANSI, BS)
Bespoke gaskets to drawings or samples
Various envelope types and insert materials
Small batch or production quantities

We can also assist with material selection based on temperature, pressure and chemical compatibility.

Related Sealing Products

Frequently Asked Questions

1. What is the advantage of a PTFE envelope gasket?
PTFE envelope gaskets provide excellent chemical resistance while maintaining strength and resilience through the internal insert.
2. Where are PTFE envelope gaskets used?
They are commonly used in chemical, pharmaceutical, food, water treatment and industrial processing systems.
3. Are PTFE envelope gaskets suitable for food applications?
Yes. PTFE is non-reactive and suitable for hygienic applications when manufactured to the correct standards.
4. What is the difference between PTFE and standard gaskets?
Standard gaskets are made from a single material, whereas PTFE envelope gaskets combine a chemical-resistant outer layer with a stronger internal core.

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