Table of Contents
- Understanding TDI vs. MDI in Polyurethane
- The Chemistry of Urethanes
- Performance & Application Comparisons
- Advantages vs. Disadvantages Side-by-Side
- Safety & Handling Considerations
- Define Key Considerations
- Frequently Asked Questions (FAQs)
- About PSI Urethanes
Understanding TDI vs. MDI in Polyurethane
The performance and durability of urethanes are shaped by their underlying chemistry, making material selection a critical step in any application. At the heart of polyurethane chemistry are isocyanates, the essential building blocks that determine how a urethane will perform under real-world conditions. Among the most widely used are:
- TDI (toluene di-isocyanate)
- MDI (methylene di-isocyanate)
Each brings its own set of strengths, challenges, and performance characteristics, making it essential to understand their differences when engineering the right solution for your needs. 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.
The PSI Standard
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 our 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.
Customization Through Chemistry
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.
Ready to engineer the right urethane solution? Let PSI Urethanes help you match material science to application demands.
Performance & Applications Comparison
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 |
| Abrasion Resistance: Impingement | MDI Polyether | TDI Polyester |
| 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 | MDI & TDI |
| 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 | MDI & TDI |
| Heat Buildup | TDI & MDI Polyether | TDI & MDI Polyester |
TDI: Simpler Structure and Higher Reactivity
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.
MDI: Greater Rigidity and Stability
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.
Advantages vs. Disadvantages Side-by-Side
TDI Pros
- Excellent resilience and flexibility, making it ideal for dynamic parts exposed to repeated stress
- Faster cure times allow for quicker production cycles and reduced downtime
- Strong high-temperature resistance and excellent compression set performance
- Cost-effective option for many general-purpose applications
TDI Cons
- Higher vapor pressure increases health and safety risks during handling
- Less suitable for extreme low-temperature environments
- Can be prone to hydrolysis in humid or wet conditions if not formulated properly
- Requires careful safety measures, which can increase overall production costs
MDI Pros
- Superior strength and durability for long-lasting performance in critical applications
- Outstanding performance in extremely low temperatures, down to -100°C
- Lower vapor pressure makes it safer and easier to handle compared to TDI
- Excellent rebound and stability under heavy loads, reducing material fatigue
MDI Cons
- Typically higher raw material costs than TDI
- More rigid molecular structure can limit flexibility in certain designs
- Longer cure times may extend production schedules
- May require specialized equipment for processing due to viscosity
Need a custom formulation for extreme environments? From flexible seals to rigid sheeting, PSI Urethanes delivers precision urethane parts built to last.
Safety & Handling Considerations
When working with isocyanates, safety is critical. Both TDI and MDI require protective measures, including proper ventilation, personal protective equipment (PPE), and strict adherence to handling guidelines.
- TDI: Higher vapor pressure means it poses a greater inhalation risk. Handling TDI requires advanced fume extraction systems and strict monitoring.
- MDI: Lower vapor pressure makes it somewhat safer, but it can still cause respiratory and skin sensitization. Protective gloves, respirators, and protective clothing are essential.
PSI Urethanes maintains rigorous safety standards. Every formulation is mixed and processed under controlled conditions to ensure employee safety and consistent product quality. We also work closely with our customers to provide guidance on proper handling of cured and uncured urethane products.
Key Considerations
When selecting between TDI and MDI urethane formulations, PSI recommends considering the following key factors:
- Operating Environment. Will the part face high heat, extreme cold, humidity, or exposure to chemicals?
- Mechanical Demands. Is flexibility, rebound, or rigidity more important for the end use?
- Production Needs. Do you require fast-curing materials for high-volume production, or can longer cure times be accommodated?
- Service Life Expectations. Is long-term durability more valuable than initial cost savings?
- Safety & Compliance. Will your facility be able to safely manage the handling requirements of TDI, or is MDI the more practical choice?
With over five decades of experience, PSI’s team evaluates these considerations alongside your application requirements to engineer the best urethane formulation for your project.
Frequently Asked Questions (FAQ)
What’s the main difference between TDI and MDI in polyurethane?
TDI is best for flexible, fast-curing parts like gaskets and bumpers. MDI in polyurethane provides greater strength, heat resistance, and long-term stability.
Is TDI more toxic than MDI in polyurethane?
Yes. TDI has higher vapor pressure and sensitization risk. MDI in polyurethane is less volatile and safer to handle but still requires strict protections.
Which one is cheaper?
TDI can carry higher costs due to safety controls. MDI in polyurethane may cost more per unit, but its durability often makes it more economical over time.
Can you use MDI in polyurethane to replace TDI?
Sometimes, depending on flexibility, cure speed, temperature, and chemical demands. Substituting incorrectly can cause rigidity, brittleness, or premature failure.
About PSI Urethanes
Since 1966, through its 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 1-866-335-5835.
What can our urethane expertise do for your next project? Connect with PSI Urethanes today to explore tailored solutions.