TDI versus MDI in Polyurethane

Urethane Parts

The properties and performance of urethanes can vary significantly based on chemistry; thus, it is important to understand what chemicals urethanes are typically comprised of in order to select the right materials for your specific application. The following explains one of the key aspects of urethane chemistry: isocyanates.  The isocyanates most commonly utilized in polyurethane formulations are TDI and MDI. TDI stands for toluene di-isocyanate and MDI stands for methylene di-isocyanate. Both TDI and MDI urethanes are advantageous to OEMs and are used in a wide range of applications across a variety of fields; however, because of their unique properties, each is best suited for specific applications. The following explains more about polyurethane chemistry as well as the physical properties of TDI and MDI urethanes.

In general, TDI offers better high-temperature resistance and performance, better compression set, and is a good option for applications with repetitive or sustained compression. For example, TDI is suitable for gaskets and bumpers. Conversely, MDI delivers excellent performance at lower temperatures –  as low as -40 to -100°C. MDI offers stronger rebound and better heat dispersal. MDI is often used for applications with extreme cold temperatures such as gaskets in an industrial freezer. Visit our website to learn more about the properties of PSI’s range of urethane formulations.

With 50+ years of experience delivering the highest quality custom urethane products, the professionals at PSI stand unequaled in helping companies in hundreds of industries around the world apply urethane products to their critical business applications. One of the reasons we stand out from the competition is out ability to help customers create a custom urethane formulation that meets the demands of their specific application. Our team has extensive experience with both TDI and MDI in our urethane formulations, enabling us to offer customers a wide range of urethane properties that will meet the challenges of your unique project. For more information on TDI versus MDI, watch our short video.

The Chemistry of Urethanes

An elastomer is a long-chain polymer, meaning that it’s made of many large molecules strung together to form long chains. In simple terms, an elastomer is an elastic material that can be stretched and when released, it will rebound to its original dimension and shape.  Each chain is made of smaller units linked together by covalent chemical bonds. These chains can easily reconfigure themselves, allowing the elastomer to return to its original shape after being stretched or put under stress. Depending on the distribution and degree of the chemical bonds of the polymer, an elastomer can have various properties.

Polyurethane is an elastomer that is formed by the reaction of isocyanate and polyol. The properties and performance of the polyurethane depend on which polyol and isocyanate are used. There are two common types  of polyols: polyether and polyester. For more information on polyols, read our short article on the difference between polyether and polyester.

While there are several others that are used in specialty applications, the most common isocyanates are TDI and MDI. The polyol is combined with an isocyanate to create a pre-polymer. The pre-polymers are cross-linked with a curative. There are dozens of chemicals used as curatives for polyurethanes and each imparts different physical properties to the finished product. It is also possible to blend curatives, thus giving us an infinite variety of formulations.

Every day, the team at PSI processes an average of seven different pre-polymers and numerous different curatives. Because we hand weigh and mix every pour, we are able to adjust the formula to meet your requirements. Processors using meter/mix machines cannot easily change formulations from product to product. For this reason, PSI offers a level of customization and expertise in urethane formulations that is unparalleled and is simply hard to find at other polyurethane suppliers.

Could your manufacturing process benefit from the durability and stability of urethane?

Contact the experts at PSI to learn more about our custom formulations for urethane including our range of isocyanates such as TDI and MDI.

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MDI and TDI Urethane Properties

Choosing the right type of polyurethane starts with understanding how the material’s chemical composition can affect your product’s performance and durability. As noted, the isocyanate selected for your urethane formulation will impact the properties of the urethane as well as what type of curatives are utilized in the formulation. The combination of TDI or MDI with either polyether or polyester will deliver a unique set of urethane physical properties as summarized below. This information is used to determine what polyol and isocyanate combination is best for a given urethane application.


  More Advantages Less Advantages
Tear Strength MDI & TDI Polyester MDI & TDI Low Cost Polyether
Abrasion Resistance: Impingement MDI Polyether Low Cost Polyether
Compression Set TDI Polyester & Polyether MDI Polyester & Polyether
Tensile (Tension) Strength MDI & TDI Polyester MDI & TDI Polyether
Rebound MDI Polyether TDI Polyester
Abrasion Resistance: Sliding MDI & TDI Polyester Low Cost Polyether
Low Temperature Properties MDI Polyether TDI Polyester
Hydrolysis (Reaction with Water) Resistance MDI Polyether TDI Polyester
High Temperature Properties TDI Polyester & Polyether MDI Polyester & Polyester
Oil Resistance TDI & MDI Polyester TDI & MDI Polyether
Heat Aging MDI & TDI Polyester Low Cost Polyether
Heat Buildup TDI & MDI Polyether TDI & MDI Polyester

About PSI Urethanes

Since 1966, through our own independent research and activity in the Polyurethane Manufacturers Association, PSI Urethanes has stayed on the leading edge of urethane technology – including developing advances in new materials, comprehensive designs, and processing technologies. Today we are among the most respected and trusted suppliers of custom polyurethane products.

We operate from our 45,000-square-foot manufacturing facility in Austin, Texas, which houses an extensive stock of polyurethane products. Our fully equipped manufacturing facility includes a versatile range of processing machinery, which allows us to work on unique, one-of-a-kind projects, as well as high volume components. Our in-house engineering, tooling, and custom mold shop, produces custom and stock production orders with exceptionally fast turn-around times. From conception to prototyping, to final production runs, our technical representatives and design engineers will work closely with your staff to meet your critical tolerances and specifications. You are guaranteed to receive experienced, professional, and personalized service from the first contact through your on-time delivery, with complete confidentiality and dedication to protecting your good name.

PSI Urethanes specializes in custom polyurethane products. Contact us today to see how we can help with your next project, or give us a call at 1-800-888-5156.