Neoprene Gaskets

Surfers and divers are very familiar with neoprene. It’s been the material of choice for wetsuits for decades. It’s also a versatile gasket material, although used in a different form to wetsuit material. Here’s what you should know about neoprene gasketing.

Synthetic Rubber

Neoprene is a DuPont tradename for polymerized chloroprene, which is one of the synthetic rubbers developed in the 1920s and 1930s. Chloroprene is composed of carbon, hydrogen, and chlorine which produce a clear liquid. Polymerization forms the molecules into long chains that interlock to create a soft, flexible material.

Neoprene is made as a solid, (described as homogenous neoprene,) and closed-cell foam. It’s this latter version that’s used in wetsuits with the pockets providing thermal insulation. Foamed neoprene provides good cushioning and is used for gasketing as it forms a soft, waterproof seal. (Pressure-sensitive adhesive applied to one or both sides makes it easier to fix in place.)

Neoprene is also used as a binder with Aramid fibers. This results in a higher-strength neoprene gasket.

Neoprene Properties for Gaskets

Being soft, (40 – 70 Shore A durometer,) and flexible with good elastic recovery, homogenous neoprene conforms readily to mating surfaces. It has excellent water resistance, (hence the wetsuit usage,) and also withstands oils, ozone, and some acids. Food grades are available.

The practical temperature range for neoprene gasketing is -20 to 180°F. This makes it unsuitable for sealing steam or other hot fluids. A bigger limitation is a lack of strength. Depending on grade, maximum tensile strength is 900 – 1,000 psi, meaning neoprene is not suitable on its own for high-pressure applications. Bound with Aramid though, it offers much higher strength.

Ask Us About Neoprene Gasketing

Homogenous neoprene comes in sheet and roll form up to 72” wide and in a range of colors. Thicknesses range from 3/32” up to 2”. We can waterjet, flash, or die-cut neoprene to the size and shape you need. If you’re looking for inexpensive gasket material and don’t need high strength, neoprene may be the gasket material for your application. Call us to discuss.

Neoprene is a synthetic polymer that resembles rubber, but as a derivative of chloroprene, it is far more durable in extreme temperatures, when exposed to oils and several chemicals, and it endures harsh weather conditions. But not all Neoprene gaskets are created equal—there are several variations or “grades” of neoprene. Each grade of neoprene gasket has its ideal application depending on factors such as temperature and pressure tolerances, the environment where it will be used, etc:

• Commercial Grade Neoprene—15-50% Neoprene mixed with other elastomers; this blend is fine for general commercial gasket applications, but not in situations where high oil resistance is necessary.
• Medium Grade Neoprene—51%+ Neoprene content; also suitable for many general manufacturing applications where a lower tensile strength will suffice.
• High Grade Neoprene—100% Neoprene is extremely resilient in the harshest, most demanding environments while maintaining its resiliency, abrasion resistance and tensile strength.
• FDA Neoprene—A mixture of Neoprene and other FDA-improved materials; gaskets made from this grade are used in the food industry, but also in many government-approved and military applications where oil resistance is key.
• PSA Ready Neoprene—Available upon request, this Neoprene has one side with a matte finish and is designed to be used with pressure sensitive adhesives.
• Nylon Cloth Inserted Neoprene—This grade is reinforced with one or two layers of nylon; good for improved creep reduction and stability.
• Diaphragm Neoprene—Polyester insertions improve performance under high pressure applications requiring high levels of oil and petroleum resistance.
• Flame Resistant Neoprene—Especially useful in potentially flammable, electric and high-heat applications, it passes the following flammability specifications: UL-94-HF-1, UL-94-HFB, MIL-R-6130C, FMVSS-302.

These grades vary in durometer ratings between 40, 50, 60, 70 and 80, can withstand temperatures between -20F to +180°F and come in sheets with several widths and thicknesses that can be cut (waterjet, flash and die cut) to exact specifications from your blueprints, or even reverse engineered.

Please contact Hennig Gasket & Seals if you have any questions about the different grades of neoprene that might best fit your application: 1-800-747-7661. We can custom manufacture any neoprene gasket you need to the most accurate specs possible.

Possibly the most widely used (and certainly the type we’re asked for most), neoprene gaskets are a good choice in many applications. However, they do have some limitations. It’s easier to understand when and when not to use neoprene gaskets if you know something about the material. Here we’ll answer: What is Neoprene? What makes neoprene so useful in many gasket applications? And when you should look for something else.

Rubber-Like Elastomer

In the 1930’s and ‘40’s scientists cooked up several types of artificial rubber. Styrene-butadiene rubber (SBR) and nitrile-butadiene rubber (NBR) are two of the best known. A third was neoprene. Like NBR and SBR, it’s mainly carbon and hydrogen, but has chlorine added to each molecule. That makes its chemical name chloroprene, or polychloroprene once polymerized. The ASTM D1418 designation for neoprene, which was DuPont’s tradename, is CR. The ASTM D2000 type and class is BC and BE, depending on the specific grade.

Useful Properties of Neoprene

The first ASTM D2000 letter tells us the upper-temperature limit of neoprene is 212°F (100°C). The lower temperature limit is around -30°F (-34°C), although neoprene becomes stiffer before getting that cold. The second letter indicates that it is prone to swelling when exposed to oils.

Neoprene does, however, resist attack by mineral and vegetable oils. It’s also resistant to ozone and weather aging, making it useful in outdoor applications.

It takes relatively little force to deform, which helps make neoprene gaskets versatile. Shore A durometer numbers are typically 50 – 70, meaning it’s quite soft. (Learn more about Shore and Durometers in, “Understanding Gasket Material Hardness” and “Measuring Gasket Material Hardness.”)

Neoprene Limitations

Aromatic hydrocarbons like benzene and toluene will degrade neoprene, as will ketones and chlorine-based chemicals. While it has many uses, neoprene should not be used with food.

Neoprene Material Forms

Neoprene gaskets are typically cut from sheet material. A range of thicknesses and hardnesses are available. Neoprene can also be foamed and is available in both open and closed-cell forms. This has the advantages of lower density and greater compressibility. Hennig material specialists can provide more details.  Contact us for your custom neoprene gasket material needs.

Open an electrical enclosure and you may see that the neoprene gasket material has taken on the imprint of the door or cover. In technical terms, it’s taken a compression set. In many gasket applications compression set can lead to sealing problems, due to a phenomenon known as creep relaxation.

Introduction to creep

Apply a load to an elastic material and it compresses. This happens because unlike in a metal, the atoms are linked in a way that lets them move. In gasket materials this is good because it lets the gasket deform to take up the irregularities between the two surfaces being sealed. However, there is a downside to this compressibility.

Rubber and rubber-like materials, as used in neoprene gaskets for example, have the ability to spring back. Release the load and the material returns to its original shape, more or less. Some materials do this better than others. The issue is that the material takes on a permanent deformation, or worse still, continues to deform. This behavior is called “creep” or more accurately, “viscoelastic creep.” It’s related to both the strength of the material and the time and temperature to which it’s subjected.

When creep is a problem

In a bolted joint the compressed gasket creates the torque in the securing bolts. But as the gasket material creeps and the gasket thins, the bolts are able to relax. That reduces the torque and the joint begins to loosen.

Polyurethane, silicone and nitrile gaskets tend to have lower creep than some other materials, as quantified by testing to ASTM 38.

ASTM testing

The principle is to measure the thickness of a sample of gasket material, subject it to load, temperature and time, then release the load. The recovered thickness is measured and the difference used to calculate a percentage reduction.

Taking creep relaxation numbers into account when choosing gasket material.

As with testing to ASTM 36, the absolute test values are less important than the ability to make comparisons between gasket materials. It’s a parameter of particular importance when lasting bolt tightness is essential.