Custom Extrusions: Rubber vs Plastic

While there are significant differences between plastic and rubber, these materials can share many performance properties.

The primary quality that separates plastic from rubber is that plastic can be melted and reused. Rubber, once cured, remains a solid. For many applications, both plastic and rubber are viable options for engineers.

If you consider both types of materials, it ensures you achieve the best performance, production and pricing for your project needs.

An Engineers Perspective

When to use plastic

When a component requires hardness or rigidity, rubber is simply not able to compete with plastic materials. Rubber compounds typically can achieve a maximum durometer or score a rating of 90.

Overall, custom plastic extrusions tend to cost less, are easily extruded and can better meet certain aesthetic requirements, such as pigmentation. Plastic also may provide opportunities for achieving narrower tolerances. With creative material compounds, rubber may be developed to satisfy many of these needs.

Flexible plastic materials can include PVC, Low Density Polyethylene and TPEs. Of these, TPEs are the materials most commonly used to achieve the performance properties of rubber. This family of plastics includes TPVs, TPOs and TPUs.

When to use rubber

Rubber is often best used in dynamic applications where compression set properties are important. It can outperform many general-use plastics in harsh operating environments. The temperature range for silicone components, for example, can reach as high as 450° F. That is far above the range of comparable plastic materials. EPDM is also a relatively low-cost rubber that offers outstanding UV, weather and ozone resistance and is ideal for outdoor applications.

Rubber may be able to better resist certain chemicals, but this should be reviewed on a case-by-case basis. If sound and vibration dampening is necessary for an application, rubber is often preferred.

Making the Choice

There are simply too many variables to say one material will always outperform the other. The decision will be unique to the specific conditions of each application. For instance, it is possible that TPV could effectively replace an EPDM seal while offering lower weight or improved aesthetics. On the other hand, EPDM may be the more cost-effective choice.

The important thing is to not limit yourself to just rubber or plastic options based on the capabilities of a manufacturer. Cooper Standard engineers have experience with both types of materials and can help you make an informed decision.

Joining plastic and rubber

iDea Seal Technology Often, an application calls for a component that has both rigid and flexible features.

For instance, a dual-durometer seal may have a rigid portion that is inserted into a channel and a flexible bulb that achieves dynamic sealing properties. Rubber and plastic do not have the compatibility to be co-extruded, so the most common solution is to combine either rigid and flexible plastic or sponge and dense rubber.

Another option is to combine plastic and rubber. Cooper Standard's iDea® Seal products feature a sponge or dense EPDM bulb chemically bonded to a plastic base. These products can easily slide into a channel and will not stretch. Plastic and rubber may also be joined through a mechanical connection. Many times, this involves attaching a plastic extrusion to a rubber component using fasteners such as plastic rivets.

A rubber component also can be designed with a dense base that fits into a channel on a plastic extrusion, effectively creating a single part. To learn more about if rubber or plastic is the right fit for your next project, contact a Cooper Standard engineer.