Gasket Material

Fiber Gasket Material – It’s Broad Meaning

Although the word “fiber” is often used to describe sheet gasket material, fiber gasket material is a very broad category. In this blog post we’ll explore what types of material count as “fiber” and when and why you might want to use them.  Hennig Gasket & Seals is gasket material suppliers of all types. 

Two Main Categories of Fiber Material

Fiber” can refer to vegetable fiber gasket material, or to sheets composed of fibers bound in an elastomeric matrix. Each provides varying levels of the temperature and chemical resistance, strength, and conformability needed in a good gasket, but there are differences between them. What’s more, within each category there are many variations of composition.

In addition, “fiber” can also mean ceramic fiber or cellulose-based gasket material. Those are quite specialized and won’t be covered here, but if you’re interested in them the specialists at Hennig Gasket  can help.

Vegetable Fiber Gasket Material

This material is made by a similar process to papermaking. Plant material is crushed and pulped to leave a mass of fibers. These are spread and dried as sheets.

Vegetable fiber gasket material, often referred to as “Detroiter” material, is very thin and has good dielectric properties. It’s resistant to water, air and most fuel oils, as well as gasoline and benzine. Adding cork to the mix results in a thicker, more compressible material.

Compressed Fiber Gasket Material

This is made by mixing aramid fibers in an elastomer like NBR or SBR, then rolling it into sheet form. Aramid is a contraction of aromatic polyamide, which is a high-strength synthetic polymer. (One of the tradenames it goes by is Kevlar.)

In gasket applications aramid supplies strength and temperature resistance while the elastomeric binder provides compressibility. Manufacturers tailor the material to specific gasket applications through elastomer selection and by varying the amount of aramid used.

Compressed fiber gasket material offers strength, good compressibility, and creep-resistance. Chemical resistance depends on the type of elastomer incorporated. As gasket material suppliers of a wide range of compressed fiber gasket material from well-known manufacturers like Garlock, Klinger, UTEX, Flexitallic and JM Clipper, we have the material to accmodate your application needs.

Thermoseal C4401: An (Almost) Universal Gasket Material

Gaskets seal everything from pipe flanges to manways but there’s no single gasket material that can do everything. However, Thermoseal C4401, (also known as Klingersil C-4401,) comes close. Here’s a quick review of how to select gasket material and an introduction to this versatile choice.

Factors to Consider

For every sealing application, a first step is to work out what material to use. This entails considering the temperature, environment, media, and pressure that the gasket will experience. (The mnemonic “TEMP” might help you remember this list.) Once those are known a gasket material can be chosen.

TEMP Compatibility Challenges

All gasket materials have a limited temperature range. Environmental concerns relate to things like exposure to ozone, UV light, and water. The media is the fluid being sealed in the pipe or outside the enclosure or man-way. And the pressure is the force the gasket will be exposed to.

Of these factors, media may pose the biggest sealing challenge. Every gasket material resists attack by some chemicals but is susceptible to others. EPDM for example is acetone-resistant but vulnerable to many fuels and oils. (Those examples are taken from “Gasket Material Compatibility Chart for Chemicals”.)

Meet Thermoseal/Klingersil C-4401

Thermoseal C4401 is one of a family of compressed fiber-reinforced gasket materials produced by KLINGER Thermoseal. These are made by mixing fibers into a rubber-like binder and then rolling it into a sheet. The fibers provide strength while compressibility and recovery come from the binder.

In Thermoseal C4401 the binder is a nitrile rubber and the fibers are aramid. Aramid is a light and strong synthetic fiber that resists abrasion and solvents. Nitrile is a form of synthetic rubber with excellent elastic behavior and good oil resistance. When combined the result is a gasket material that withstands temperatures as high as 750 °F (399 °C), and withstands a long list of chemicals.

Ask About Thermoseal/Klingersil C-4401

If you’re unsure about the media you’re sealing or just looking for a universal gasket material, C4401 is an excellent choice. Specialists at Hennig Gasket & Seals will be happy to tell you more.

Gasket Materials for Washdown Environment

Cleaning is important in many industries, but pharma and food and beverage have it down to a fine art. For those sectors frequent intensive washdowns are a way of life and equipment gaskets must be up to the task. Silicone gasket material and neoprene gasket material are, open-cell foams are not. Here’s some detail.

The Washdown Process

Water heated to 170°F is blasted at 1,500psi of pressure to remove every trace of dirt and contamination. For extra-thorough cleaning caustic chemicals might also be added, creating an even more challenging sealing environment.

NEMA and IP Ratings

Enclosures are rated for the “ingress protection” they provide. NEMA is the US system while elsewhere they like the “IP” categories. A NEMA 4 rating, broadly equivalent to IP66, means an enclosure is designed to resist jets of high-pressure water from a hose. In other words, washdown. A step up in protection is NEMA 4x or IP69k. NEMA 4x protects against aggressive chemicals while IP69k is a rating for steam jet cleaning.

Gasket Materials for Washdown Environments : EPDM, Silicone, Neoprene

First, note that equipment and enclosures should be designed in a way that prevents water jets from directly impinging on the gasket material. Even with that though, the gasket outer surface is still going to get soaked.

This is why open-cell foam is not appropriate. It’s going to let water soak through to the interior. Closed-cell foam is better and solid better still, (though not as soft or compressible.)

Second, the gasket material must resist attack by hot water, possibly incorporating caustic chemicals. Good candidates are EPDM, silicone, and neoprene. Some points to note about each of these are:

  • EPDM gasket material is also UV-resistant. That makes it a good choice outdoors and wherever UV light is used.
  • Silicone gasket material is flexible from –100 to 500°F.
  • Neoprene gasket material works over a range from -40 to 250°F. It also has good oil resistance but is attacked by ozone.

Ask the Experts

You should know the strengths and limitations of the gasket materials you’re considering. The specialists at Hennig Gasket have a lot of knowledge and experience. Call them or reach out by email.

Garlock Gasket Material – A Trusted Name

Trust takes time to earn but can be lost in seconds. That’s why people stick with brands that have served them well. Why risk something new when you already know what works? For this reason, many gasket buyers specify Garlock gasket material. Either they’ve had good experience with it or they know someone who has.

About Garlock

Garlock has been around for over a century, so they’re doing something right. While their business is sealing, Garlock focuses on the benefits gaskets deliver: keeping people safe and helping businesses be more profitable.

One hundred years ago we used natural materials like rubber and leather but industrial processes have changed since then. Today, increased temperatures and pressures demand gasket material that’s stronger and more resilient.

Garlock invests heavily in R&D to develop innovative materials that meet these challenges. Their research and testing facilities are state-of-the-art and they have a strong environmental commitment. Together, this ensures Garlock gasket material stays at the forefront of sealing technology.

An overview of Garlock gasket material

Whether you’re dealing with extreme temperatures, high pressures, vacuum or aggressive chemicals, there’s a Garlock material to suit. Scan their product catalog, (or speak with a Hennig specialist,) and you’ll discover PTFE in many grades, graphite, compressed fiber, and natural and synthetic rubber gaskets and gasket material.

Brand names you may be familiar with include GYLON® restructured PTFE, GRAPH-LOCK® flexible graphite sheet, BLUE-GARD® compressed rubber and THERMa-PUR Extreme Temperature material.

Known for excellent chemical resistance, GYLON® is used in many industries including pharmaceuticals and food processing. GRAPH-LOCK® is a high-temperature material with good creep-resistance. BLUE-GARD® also offers a wide temperature range and is available with a range of rubbers. THERMa-PUR, however, beats them all as it will operate at temperatures as high as 1,832°F (1,000°C).

A reputation you can trust

When a business endures you know it’s doing something right. Garlock isn’t the only company to make gasket material, but they’ve been at it a long time and make a quality product. If you’d like to use Garlock gasket material in your next project, speak to us.

Gasket Material Selection

It’s said that what comes out of the joint is what goes back into the joint, but sometimes we’re asked if there’s a better material to use. That’s because the expense of replacing a gasket often far outweighs the cost of the part. When that’s the case a little extra spent on better gasket material might save a lot.

Unfortunately, there’s no easy answer to the material question. All we can say is, “It depends.” Here’s why, along with some guidance on selecting the best gasket material.

Four Key Criteria

It’s impossible to determine an appropriate material without knowing the temperature, environment, media and pressure the gasket will experience. It’s also important to determine the actual range of every parameter and every operating condition. Cleaning with caustic agents, for example, creates very different gasket challenges than handling a benign fluid like milk.


This refers to the temperature of the media. Many elastomers harden when cold, making them less able to resist pressure and reducing their ability to flex as the joint changes size. Neoprene, for example, has a lower limit of -40°F while high-performance fluoroelastomer (FKM) only goes to -10°F.


Temperature is one factor, sunlight another. A gasket used outdoors in a midwestern winter could see low temperatures while one exposed to the desert sun will get extremely hot. In addition, UV light damages some common gasket materials. NBR, for example, has poor UV resistance while EPDM holds up much better.


Some gasket materials suffer swelling when exposed to oils and other will oxidize rapidly. Brake fluid is incompatible with nitrile rubber and FKM while silicone and EPDM are a poor match for gasoline.


The pressure inside a pipe or enclosure can force gasket material to extrude out sideways. Harder materials generally hold up better but require higher clamping forces. In extreme cases, it may be necessary to consider PTFE, spiral-wound or metal gaskets.

Seek Advice

Every gasket application is different and it’s never easy to say which is the best material to use. Start by determining the four criteria listed above, then consult a material specialist.

Oxygen Compatible Materials

Many industries use oxygen. It’s one of the most reactive elements, which makes it useful in processes from steelmaking to paper production as well as healthcare and waste treatment. This reactivity, (a willingness to form chemical bonds with other elements,) also creates sealing problems. Here’s an overview of the challenges posed by oxygen and a discussion of the best gasket materials to use.

The Air We Breathe

Oxygen is one of the most plentiful elements and makes up some 20% of the air we breathe. It’s also locked into the oceans as water. At temperatures above -297°F (183°C) it’s a gas. Oxygen has a strong affinity for electrons, which is what lets it bond readily with many other chemicals. Rust and oxidation are the common results, although fire and explosions are always possible.

Oxygen Production

Oxygen is produced by cryogenic distillation or pressure swing adsorption (PSA). As the name implies, the cryogenic process entails cooling air until it becomes liquid, allowing the oxygen to boil off. This produces a very high purity gas.

PSA involves pushing air through aluminosilicate minerals. These take up the nitrogen, leaving just oxygen, but at a lower purity than the cryogenic process.

Keeping Oxygen Systems Clean

Given that oxygen is highly reactive, it’s essential that any surface it touches is clean. Some industries have special requirements for oxygen-clean surfaces. The standards applicable to your industry will specify the type and degree of cleaning needed.

Materials for Gaskets in Contact with Oxygen

Liquid oxygen can only be sealed by materials capable of withstanding very low temperatures. PTFE gaskets are a good choice as is FFKM (perfluoroelastomers) gasket material.

Good gasket materials for gaseous oxygen include neoprene, EPDM, silicone, butyl and Viton® (a DuPont brand name for FKM.) Rubber materials such as SBR and natural rubber should be avoided because of their tendency to react with oxygen.

Ask an Expert

Always consider temperature, pressure and the environment along with the media being sealed. For this reason, it’s prudent to consult with a materials specialist before ordering gaskets or gasket material.

Weather Resistant Gasket Material Selection

Weather is hard on gasket material, thus identifying a weather resistant gasket material is important. Ultraviolet (UV) rays in sunlight attack bonds between carbon atoms in many rubbers. Ozone, (O3) often found in polluted industrial areas and around electrical enclosures, does the same. Temperature extremes, especially cold, affect material performance, as can moisture.

Open vs Closed-Cell Gasket Material

Open cells will absorb moisture. If temperatures drop to freezing the subsequent expansion could quickly destroy the material. Always choose closed cell material for a gasket that’s likely to get wet.

Materials to Avoid in Outdoor Applications

Inexpensive nitrile rubber/NBR, often selected for its good oil and solvent resistance, is not a good choice for weather resistant gasket material. The same goes for SBR. Nitrile gasket material is poor with both O3 and UV light, although water resistance is quite good. Its low-temperature limit is around -30F (-34C).

Better Weather Resistant Gasket Materials

Neoprene is a popular choice for gasket material but is not recommended for outdoor use. While it can handle a wide temperature range and offers moderate weather resistance, O3 resistance is poor.

Best Weather Resistant Gasket Materials

A little more expensive than Neoprene, EPDM is good for outdoor gasket applications not involving exposure to oils or solvents. EPDM provides a combination of good O3, UV, and general weather resistance.

Like EPDM, silicone gasket material resists attack by O3, UV, and general weather resistance, but also has excellent fungal and biological resistance. (Sometimes relevant in humid climates.) It has a wide temperature range but poor abrasion resistance is a limitation in applications with a significant joint movement or frequent opening. Silicone also suffers from high gas permeability and is not recommended for use with ketones, petroleum or chlorinated solvents.

For superior outdoor performance, fluorosilicone materials stand out. These have excellent resistance to O3, UV, and weather plus a very wide temperature range. They are also good with fuels. Their main limitations are poor abrasive performance and high price.

Gasket Material Selection Advice

Always consider the application environment when choosing weather resistant gasket material. Outdoor locations expose a gasket to UV light, weathering, and possibly O3. Extremely low temperatures can also be a problem. Hennig Gasket material specialists can provide further advice.

Gaskets for Low Temperature Applications

A common mistake when selecting gasket material is to consider only the upper temperature limit. Excessive temperatures can lead to gasket failure, but so too can low temperatures. The Challenger Space Shuttle disaster is perhaps the best known example of this.  Low temperature elastomers are worth looking at.

Gradual Transition

Metals are either solid or liquid with no fuzzy middle ground. Elastomeric materials like neoprene and SBR don’t have this clear melting/freezing point. They just become harder or softer. The dividing line is called the Glass Transition Temperature (Tg), but the difference in material behavior either side can be quite subtle. This makes it difficult for manufacturers of gasket materials to specify strict minimum temperatures. Instead, you’re more likely to see a range.

Elastomers and Low Temperatures

Low temperatures are a problem for elastomeric gasket materials, for two reasons:

  1. The lower the temperature the more the elastomer resists deformation under load. That’s bad because the material needs to squash into the faces being sealed.
  2. Low temperatures change compression set performance. A cold gasket material can take on a compression set and then leak as temperatures rise. (This is essentially what happened with the Challenger.)

Defining “Low”

In gasket terms, low temperatures are those which might be reached during winter in the upper Midwest. That means -20° to -40°F, which is far above the kind of cryogenic temperatures seen when processing and storing liquefied gases.

Gasket Material Selection

For very low temperatures, those down to -300°F, PTFE/Teflon gaskets are usually the material of choice. However, Teflon does tend to creep, making it unsuitable for some applications.

Silicone gaskets stay flexible at temperatures down to -80°F with some grades reaching -100°F. Nitrile rubber gaskets will typically work down to -80°F, although it’s important to check the material specs for details. Other elastomers harden before getting that cold, so always check material specifications.

Consider Both Temperature Extremes

Low temperatures can be as much of a problem for gasket materials as high temperatures. The loss of the Challenger serves as a reminder that gaskets may be exposed to temperatures below design limits.

Contact Hennig Gasket & Seals for your low temperature elastomer needs.

The Role of Gaskets in Minimizing Fugitive Emissions

Fugitive emissions are a serious matter for chemical plants and petrochemical facilities. First, the EPA is focused on reducing unplanned releases of VOC’s into the atmosphere, and second, it’s a cost-saving opportunity. Studies blame valves for the bulk of these emissions, but flanged joints and their associated gaskets play a part too.

Hunting Fugitives

Defined as “… unanticipated or spurious emissions from any part of the process plant,” in 2014 the Fluid Sealing Association estimated fugitive emissions amounted to some 300,000 tons annually. Furthermore, it’s thought a high proportion are hydrocarbon gasses like methane believed to be environmentally harmful.

Plants handling such chemicals are expected to implement Leak Detection And Repair (LDAR) protocols, preferably on a monthly basis. “Sniffing” technology is the method most commonly employed, although IR camera technology is increasingly available.

Prevention First

Should a LDAR survey reveal a leak the next step is usually to shutdown the affected equipment for valve repair or gasket replacement. Unplanned shutdowns are disruptive and expensive, making it essential to avoid such events. While leak-free performance can never be guaranteed, buying different types of quality gasket materials and following good sealing disciplines will reduce the likelihood of problems.

Three Principles to Follow

  • Select material appropriate to the media, pressure and temperature. Nitrile gasket material for instance is generally compatible with hydrocarbons like gasoline but should not be taken above 250°F. A neoprene gasket will perform better against ammonia, alcohols and mild acids while high temperature applications may need a fluorocarbon or PTFE gasket. In particularly arduous conditions a spiral wound gasket might be needed.
  • Analyze the joint to determine material thickness and hardness needed. The general rule for gasket materials is “as thin and soft as possible.” The goal is always to ensure the gasket compresses sufficiently to seal the gap when the joint is bolted up. High bolt loads risk deforming the flange, potentially causing leaks.
  • Follow good gasket replacement disciplines. Clean flanges thoroughly and verify mating surfaces are undamaged. Tighten bolts following the recommended sequence to avoid uneven compression and the risk of gasket extrusion.

Failure Mechanism at High Temperatures

Previous blog posts emphasized the importance of assessing the peak temperatures anticipated in a gasketed joint. Left unsaid has been why this matters. It’s probably obvious that polyurethane, nitrile and silicone gaskets all have a temperature at which they melt. More important, all will likely fail under prolonged exposure to temperatures near their melting point, due to a phenomenon called “creep.”.

Viscoelastic materials

Most gasket materials are viscoelastic. The “viscous” part means they have a propensity to flow slowly, like a thick gel and “elastic” refers to their ability to stretch and return to their original dimensions. However, elasticity has its limits. If the material is stretched too far it can’t return to its original size or shape, resulting in permanent “plastic deformation.”

Place a viscoelastic gasket material like polyurethane under load and it becomes thinner while simultaneously spreading outwards. This is “creep.” Releasing the load lets the material recover, but only to the extent that it has not been deformed plastically.

Creep relaxation

In a gasketed joint the material is compressed, either by the stretch of the flange bolts as they are tightened or by other retaining clamps. When first placed under load it starts to creep, but as the gasket thins the load lessens until the creep stops. This is termed creep relaxation. With good design this happens before the gasket reaches a point where the joint starts to leak.

Higher temperatures

Creep is related to temperature. When a polymer like polyurethane or styrene butadiene rubber gets warmer the molecular chains slide more readily. As a result it takes less force to produce a given movement. As the temperature approaches the melting point of the material, the force needed to produce a given movement falls quickly. To take one example, this means that at temperatures over 200 F (93 C) a nitrile gasket starts shows considerable creep.

Consider the material properties

Always select gasket material with the knowledge of the maximum temperatures expected. The more safety margin can be incorporated the less creep will be experienced, leading to a longer lasting gasket.