Introducing Filled Grades of PTFE Material

Mar 04, 2026

PTFE is known for a wide working temperature range and resistance to a broad spectrum of chemicals. It’s also very soft, unless reinforced with a filler. Fillers increase strength and creep resistance, but change where and how the material can be used. This blog reviews the reasons for choosing PTFE and discusses the main filler materials and their benefits.

PTFE Characteristics

Virgin PTFE withstands temperatures as high as 500°F (260°C) and remains flexible down to -430°F (-257°C). It’s also chemically inert, resisting attack by almost all acids and alkalies other than fluorine or nitric acid. In some applications its low friction is an asset, but it does tend to wear.

However, very low tensile strength (2,900 – 5,000 psi) and minimal elastic recovery, limit applications to those where creep won’t be a problem. These tend to be in the food industry where the advantages – it doesn’t impart any taint and is not hazardous if ingested – outweigh the design constraints it imposes.

Adding Fillers to Virgin PTFE Material

Tensile strength is raised by adding fillers. These reduce its tendency to creep and widen the range of potential applications. However, most filled grades lose their FDA “food grade” rating.

The properties of filled grades are strongly influenced by the characteristics of the filler material. Here’s an overview of those most widely used.

Glass: Chemically-inert with much less propensity to creep. Can be abrasive.
Carbon: Has increased wear resistance and higher thermal conductivity. Provides enough electrical conductivity to dissipate static.
Graphite: Lowers friction, but unlike carbon, does not increase wear-resistance.
Molybdenum Disulfide (MoS2): Reduces friction and increases wear-resistance. Often used in PTFE dynamic seals.
Bronze: Provides thermal and electrical conductivity and increases wear-resistance, but lowers chemical resistance.

Get Help When Selecting PTFE Material

When a gasket application needs excellent chemical resistance, PTFE often tops the candidate list. It’s important to consider though, that virgin PTFE material is soft and easily deformed. This can be addressed by using one of the filled grades.

Fillings alter properties like friction and wear-resistance. This should be considered during the material selection process. Specialists at Hennig Gasket & Seals are always happy to help.

PTFE Gaskets

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Materials for Washer Gaskets

Feb 03, 2026

People don’t usually consider washers a type of gasket, but depending on how they’re being used, that’s exactly what they might be. This blog discusses what washer gaskets do and what to consider when selecting material for them.

Washers for Sealing

A washer is a ring of material under the head of a bolt or under a nut. In fastening applications it’s job is to spread the load being applied. A washer gasket is a ring of gasket material placed under a bolt head or nut. Gasket material isn’t a good load spreader because it’s soft and compressible, but it can have three other functions:

Seal against fluids
Dampen transmission of noise and vibration
Prevent galvanic corrosion

Another way washers, felt washers specifically, are used is to lubricate a rod or shaft passing through the washer. This works because felt washers are very good at retaining oil.

Washer Gasket Material Options

Like any gasket, a washer gasket has to take up deformations in the surfaces it’s sealing. This requires compressibility. Recovery, or resistance to compression set, may be another useful property if the bolt is likely to get hot and expand.

Other selection criteria relate to the media being sealed and the environment the washer gasket will go into. This means looking at characteristics like tolerance to oils, acids and alkalies, and UV and ozone. Then consider temperature, both of the media and the environment.

For dampening applications the vibration-attenuating properties of the material are what matter most. This is where a knowledgeable supplier can be a big help.

Galvanic corrosion occurs when metals with different electrolytic compatibilities come into contact in the presence of moisture. For this type of application the washer gasket’s job is to be an insulator between the two metals.

Depending on the application and the temperature range needed, good material choices can be:

PTFE
Neoprene
EPDM
Silicone
NBR
SBR

Advice From Hennig Gasket & Seals

With many different materials to choose from, deciding which is best for an application can be quite daunting. A risk-free approach is to consult the specialists at Hennig. Contact us today.

Flange Gaskets

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Advantages of Silicone for Customer Gaskets

Jan 07, 2026

When choosing material for a custom gasket application, going through the temperature, environment, media and pressure criteria may leave you with a few options. Silicone probably won’t be the cheapest, but it could be the most cost-effective. Here’s when and why to consider custom silicone gaskets.

Excellent Sealing Properties of Silicone

Silicone remains flexible from -94 to 392°F (and withstands temperatures up to 500°F for short periods). It takes a very low compression set, retaining its ability to seal over hundreds of opening and closing cycles. It’s tensile strength is up to 1,100 psi.

Silicone Material Broad Chemical Compatibility

Silicone repels water and resists attack by ozone and UV light, making it a good gasket material for outdoor applications. Being chemically inert, It resists weak acids, most alkalies and hydraulic fluids and oils. Where it performs less well is in resisting attack by strong acids and solvents.

Available in Multiple Grades and Material Thicknesses

Silicone gasket material is produced in sheet form with thicknesses up to ¼”. (Contact us if you need thicker.) It’s made in a range of formulations with various hardnesses and strengths. Colored silicone is available, as are FDA and medical grades.

For greater compliance in lightly-loaded sealing applications, consider using closed or open cell silicone foam.

Size and Shape Options

Custom gaskets often need very specific or unusual features or dimensions. Ask your custom silicone gasket maker what processes they have and about their size and shape capabilities.

At Hennig Gasket & Seals we use waterjet cutting for especially challenging gaskets. Waterjet yields a very smooth edge and can cut features as small as ¼” diameter. Flash, die and hand cutting are also available, depending on quantity required.

Silicone, For Long-Lasting Gaskets

Besides offering a wide temperature range and good chemical resistance, silicone makes a very durable material. If you have applications where a joint, cover or door will be opened and closed multiple times, silicone will probably continue to seal longer than other materials. This can make it very cost-effective when compared to materials like EPDM, neoprene and nitrile. Contact us to learn more.

Silicone Gaskets

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EPDM vs. Viton Gasket Material

Dec 27, 2025

For a wide temperature range and good chemical resistance, many gasket material buyers think they have to specify Viton®. There are times when this is the right choice, but sometimes it isn’t. For many applications EPDM is a better material. This blog does an EPDM vs Viton comparison so you can decide which to use.

Chemical Comparison

EPDM gasket material and Viton gasket material are both flexible elastomers suitable for sealing gaps and joints in a wide range of applications, but chemically they are quite different. Viton is a tradename for a family of fluoroelastomers that go by the acronym FKM. EPDM, (Ethelyene Propylenen Diene Monomer), is hydrocarbon-based. During manufacture EPDM is cured with either sulfur or peroxide. Peroxide curing raises strength and the upper temperature limit.

Viton was developed by DuPont and is now a Chemours product. Chemically, its main feature is the presence of fluorine. This bonds with carbon to provide excellent resistance to chemical attack.

Property Comparison

Temperature range: Viton is flexible from -4 to 410°F. EPDM works from -60 to 225 or 300°F, depending on curing process.
Strength: Viton and EPDM are similar with a tensile strength of around 1,000psi. Peroxide-cured EPDM is stronger, up to 3,000psi.
Compression set: Both materials perform well.
FDA grades of both are available

Chemical Resistance

This is where the two diverge. EPDM resists:

UV
Oxidation
Acids
Alkalies
Ketones
Water and steam

Limitations are hydrocarbons and petroleum fluids, which cause swelling.

Viton resists most chemicals, except ketones, and organic acids. The latter, (substances like acetic, citric and tartaric acids), occur in food and beverage processing.

When to Use

EPDM works well in outdoor applications. It’s often used for weather stripping and dust covers, as well as mounts of various types. Another application is for low pressure boiler gaskets. FDA-grade EPDM is used in food and beverage equipment.

While Viton can be used in food processing, (subject limitations mentioned above), its main use is in fuel-handling equipment like pumps and valves. It’s also used in a lot of chemical processing equipment.

Expert Advice is Available

Specialists at Hennig Gasket and Seals are always happy to discuss gasket material applications. Contact us and let’s talk!

Gasket Material

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Understand What SBR Rubber Means

Feb 15, 2025

If you’re looking for a flexible, inexpensive, abrasion-resistant material, SBR rubber should be on your list of candidates. In this blog we’ll explain what it is, when you might use it, and what “SBR” means.

SBR Chemistry

SBR is an acronym for Styrene Butadiene Rubber. It’s a hydrocarbon-based synthetic material developed in the 1940s as a response to limited availability of natural rubber.

As the name implies, SBR has two primary constituents, styrene and butadiene, plus some curatives and fillers. Styrene is derived from petroleum, and is a clear liquid composed of small molecules. Butadiene is a gas at room temperature and is obtained from crude oil or natural gas.

When polymerized, the two combine into long chains. If the resulting soft, sticky material is then held at an elevated temperature, (a process called vulcanization), links form between these chains that increase strength and hardness.

Properties of SBR

Developed as a natural rubber substitute, SBR has very similar, although slightly superior, properties. It’s flexible at temperatures from -40 to 180°F (-40 to 82°C), whereas rubber becomes brittle at temperatures below freezing. It’s also very abrasion-resistant, has good elastic recovery, and resists taking a compression set.

Most SBR is produced with hardness in the range of 50 to 80 Shore A. Tensile strength is 400 to 1,000 psi, although this can be increased with fabric reinforcement or by adding suitable fillers.

As for chemical and environmental compatibility, it resists most acids, plus brake fluid and water. It is however, attacked by oils and other hydrocarbons. Ozone resistance is better than that of natural rubber, although still not particularly good.

Uses for SBR

One of the biggest applications in terms of tons produced is car tires. Industrial uses include conveyor belts, bumper pads, couplings, and gaskets and seals. We stock SBR in sheet form in various thicknesses and widths and can cut it to the shape you need.

So, to recap, if you’ve ever wondered about the meaning of SBR rubber, just know that it’s like natural rubber, only without the low temperature problem and ozone sensitivity.

Rubber Gaskets, SBR Gaskets

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When Should You Ask for Butyl Rubber?

Jan 15, 2025

Synthetic rubber materials like SBR were developed to increase the supply and compensate for the limitations of natural rubber. For most of these man-made elastomers, while they excel in some regards, they fall short in others. Poor weather and ozone resistance are two of the biggest weaknesses.

Butyl rubber is a synthetic material that plugs this gap. Suitable for a range of sealing applications, it also has great damping and permeability characteristics. Here’s a closer look.

Butyl Rubber Basics

As polymerized at the factory, butyl rubber is white or colorless. It’s usually blended with carbon black to make it black, although other colors are possible.

Butyl rubber is much more dense than other synthetic rubbers, so it’s heavier, but this means it’s a very good absorber of vibration. The same chemical structure that creates high density also renders it impermeable to liquids and gases. (Other synthetic rubber materials like SBR and EPDM have a degree of gas permeability.)

Butyl rubber is on the softer side, (It’s available with Shore A ratings of 40 to 90 but is usually around 65), and has a working temperature range of -40 to 285°F. It’s also resistant to water, dilute acids, and animal and vegetable oils.

Limitations of Butyl Rubber

Butyl rubber will tend to take a compression set, limiting its use as a gasket in applications where the joint will be opened up periodically. Its abrasion resistance is only moderate and it is attacked by hydrocarbon fuels and oils.

Good Applications for Butyl Rubber

The biggest market for butyl rubber is automobile tires, where it’s used as a liner material. In terms of seals and gaskets, applications include:

Tank liners
Pond liners
Cushioning
Shock absorbers
Flange and full-face gaskets, especially for outdoor applications

Butyl Rubber Sheet Cut to Shape

Ask for butyl rubber when you need impermeability, weather-resistance or cushioning. Hennig Gasket & Seals has it in sheet form and a range of thicknesses. We can die, flash or waterjet cut it to the exact size and shape you need. Contact us to discuss your needs and get a quote.

Flange Gaskets

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EPDM Gaskets vs. Viton Gaskets

Jan 07, 2025

Chemical Comparison

Viton was developed by DuPont and is now a Chemours product. Chemically, its main feature is the presence of fluorine. This bonds with carbon to provide excellent resistance to chemical attack.

Property Comparison

Temperature range: Viton is flexible from -4 to 410°F. EPDM works from -60 to 225 or 300°F, depending on curing process.
Strength: Viton and EPDM are similar with a tensile strength of around 1,000psi. Peroxide-cured EPDM is stronger, up to 3,000psi.
Compression set: Both materials perform well.
FDA grades of both are available

Chemical Resistance of EPDM and Viton Gaskets

This is where the two diverge. EPDM resists:

UV
Oxidation
Acids
Alkalies
Ketones
Water and steam

Limitations are hydrocarbons and petroleum fluids, which cause swelling.

Viton resists most chemicals, except ketones, and organic acids. The latter, (substances like acetic, citric and tartaric acids), occur in food and beverage processing.

When to Use

Expert Advice is Available

Specialists at Hennig Gasket and Seals are always happy to discuss gasket material applications. Contact us and let’s talk!

Flange Gaskets

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Selecting Materials for Rubber Washers

Dec 15, 2024

Rubber washers are used for two types of application: sealing and vibration damping. Another use is load-spreading in fastening applications, but this usually requires metal, so isn’t covered here. What is covered are some principles to use when selecting washer material and an overview of the materials available. First though, what are washers and where are they used?

Rubber Washer Basics

A washer is a disc-shaped piece of thin material with a hole through the center. The hole typically takes a screw or bolt, the head of which is bigger than the hole and fits over the washer.

One category of applications is sealing, typically in faucets and valves. In use the washer creates a seal against a mounting face to close off the flow of fluid. The washer material needs abrasion resistance, because it slides against the face as the valve is closed, and good recovery so it springs back to its original dimension.

The other category is vibration damping. Circuit boards are a good example. A screw through a hole in the board mounts it to the chassis. A rubber washer between the screw head and the board provides security while reducing vibration from the chassis.

Material Selection Guidelines for Rubber Washers

When selecting rubber washer material, consider:

Temperature – the range the material will see
Environment – exposure to sunlight, ozone
Media – the fluid being sealed
Pressure – the loads being applied

Materials for Rubber Washers

“Rubber” is a generic term for elastomers that are flexible and compressible at room temperature. Materials that can be used, subject to the criteria listed above, are:

Red rubber/SBR – temperature range of -22 to 158°F, good abrasion resistance
Nitrile – temperature range of -40 to 225°F, resistant to most fats, oils, fuels and water
Neoprene – good water resistance
EPDM – resists most chemicals and oils
Silicone – exceptionally wide working temperature range
Viton® – resists oils and fuels, wide temperature range

Select for the Application

Washer material should be chosen with the same care as is used for gaskets. Hennig Gasket and Seals stocks a wide range of suitable materials and can cut custom sizes to order.

Applications, Rubber Gaskets

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What to Consider for a Valve Cover Gasket

Nov 14, 2024

Valve covers can be hard to seal. That’s because they’re often made from thin material that bends as the fasteners are tightened. The result is uneven compression of the gasket material, which often leads to leaks. If you’re looking for a valve cover gasket for industrial equipment or an engine application, here’s what to consider.

Standard Gasket Material Factors

As with every gasket application, the first points to determine are:

Temperature of the media being sealed
Environment – where the gasket will be placed in service
Media – does it have corrosive properties and what gasket materials is it incompatible with?
Pressure – the load the gasket will be subjected to determines the material strength needed

Establish these and you’re on your way to determining the best material for your valve cover gasket, but there is one other point to consider.

Dealing with Deflection

If the valve cover is likely to deform as it’s tightened down the gasket material needs enough compressibility to not leave any gaps. This leads to softer, (lower durometer, in the case of elastomeric materials), and thicker materials. Softness ensures sufficient deflection while thickness matters because of the percentage deformation needed. (1/16” deflection is a smaller percentage of gasket material ¼” thick than if the material is only 1/8” thick.)

Candidate Gasket Materials

The application will determine the material. If you’re sealing a valve cover on a diesel engine with high temperatures and oil, an aramid fiber gasket might be the right choice. (Frenzelit Novatec® fiber with graphite gaskets provide good chemical resistance and handle high temperatures.)

Elsewhere, perhaps in air compressors or covers over industrial valves, rubberized cork can be effective. In select cases NBR gasket material or EPDM gasket material may work well too.

Replace, Don’t Reuse

It can be tempting to reuse a valve cover gasket when the joint was only opened up for an inspection. Don’t do this.

Most gasket materials take a compression set. This means they don’t spring back to their original thickness. The amount may be too small to see, but reusing the gasket risks leaks.

Contact Hennig Gasket & Seals for custom sealing solutions.

Applications, EPDM Gaskets

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Food-Grade Silicone Gasket Material

Oct 01, 2024

A number of gasket materials meet the FDA’s criteria for being Generally Regarded as Safe (GRAS) but the most versatile is silicone gasket material. FDA-compliant silicone rubber is a good choice for sealing and other applications in the food and beverage, medical and pharmaceutical industries. Here’s what you should know.

The Risks of Indirect Contact

Material used for gaskets and seals shouldn’t end up in food or other substances consumed by humans, but it can come into contact with them, either accidentally or by design. Solids and liquids may for example touch the seals and gaskets used in mixers, kettles and storage vessels.

If this happens, especially at elevated temperatures, there’s a risk of some of the chemicals in the seals being picked up by the foodstuff. In the best case, this might impart a taint or color but, depending on the details of the material, it could transfer potentially harmful chemicals that end up being ingested.

To avoid this, always use FDA-compliant materials wherever contact with foodstuffs is possible.

FDA Regulations

Among other activities, the Food and Drug Administration (FDA) regulates the materials used in food, beverage and pharmaceutical manufacturing. For elastomers like those used in gaskets and seals, the relevant regulation is 21 CFR 177.2600. This identifies what can and cannot come into contact with anything consumed by humans.

Some materials are considered GRAS, meaning their use is permitted. FDA-compliant silicone rubber is one such material.

Food-Grade Silicone Gasket Material

Silicone is an excellent material for gaskets. It’s soft but doesn’t take a compression set, and springs back to its original size when unloaded. It has a working temperature range of -67 to 450°F, and it resists mild acids and oils.

Food-grade silicone is almost always white, because it’s the colored additives that can result in contamination. Some buyers will ask for “white silicone” but this doesn’t guarantee it meets FDA standards. To be safe, when buying food grade silicone, always specify compliance with 21 CFR 177.2600.

We carry FDA-compliant silicone rubber in 48″ wide rolls and thicknesses from 1/32 to 1/4″. Cutting services are available.

Silicone Gaskets

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