What's the Difference?

MDI (Methylene Diphenyl Diisocyanate) and TDI (Toluene Diisocyanate) are both types of isocyanates commonly used in the production of polyurethane foams and coatings. While they are similar in their chemical structure and function, there are some key differences between the two. MDI is known for its high reactivity and stability, making it suitable for a wide range of applications. It is less volatile and has a lower risk of causing respiratory sensitization compared to TDI. On the other hand, TDI is more commonly used in flexible foams due to its excellent flexibility and resilience properties. It has a higher vapor pressure and is more likely to cause respiratory sensitization, making proper safety precautions crucial when working with it. Overall, the choice between MDI and TDI depends on the specific requirements of the application and the desired properties of the final product.


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Further Detail


Polyurethane is a versatile material widely used in various industries, including automotive, construction, and furniture. The production of polyurethane involves the use of isocyanates, which are essential components in the formation of polyurethane foam. Two commonly used isocyanates are MDI (Methylene Diphenyl Diisocyanate) and TDI (Toluene Diisocyanate). While both MDI and TDI serve similar purposes, they possess distinct attributes that make them suitable for different applications. In this article, we will explore and compare the attributes of MDI and TDI.

Chemical Structure

MDI and TDI differ in their chemical structures, which impacts their properties and applications. MDI is a diisocyanate compound with two aromatic rings connected by a methylene group. This structure provides MDI with excellent stability and resistance to heat and chemicals. On the other hand, TDI consists of two aromatic rings connected by a toluene group. The presence of the toluene group makes TDI more reactive and prone to degradation when exposed to heat and certain chemicals.


When it comes to reactivity, TDI is generally more reactive than MDI. TDI has a higher reactivity due to the presence of the toluene group, which enhances its ability to react with polyols and form polyurethane. This higher reactivity makes TDI a preferred choice for applications that require fast curing times, such as spray foams and coatings. MDI, on the other hand, has a slower reactivity, making it suitable for applications that require longer processing times, such as rigid foams and adhesives.

Physical Properties

The physical properties of MDI and TDI also differ, influencing their applications in various industries. MDI-based polyurethane exhibits excellent mechanical strength, durability, and resistance to abrasion. These properties make MDI ideal for applications that require high-performance materials, such as automotive parts and industrial coatings. TDI-based polyurethane, on the other hand, offers good flexibility, elasticity, and resilience. These properties make TDI suitable for applications that require cushioning and comfort, such as mattresses and furniture upholstery.

Toxicity and Handling

Both MDI and TDI are classified as hazardous substances and require careful handling to ensure worker safety. However, MDI is generally considered less toxic than TDI. MDI has a lower vapor pressure, reducing the risk of inhalation exposure. It also has a lower potential to cause skin sensitization compared to TDI. Nevertheless, proper safety measures, including the use of personal protective equipment and adequate ventilation, should be followed when working with either MDI or TDI to minimize potential health risks.

Environmental Impact

Considering the environmental impact, MDI and TDI have different characteristics. MDI-based polyurethane is known for its excellent durability and resistance to degradation, resulting in a longer lifespan for products made with MDI. This longevity reduces the need for frequent replacements, contributing to waste reduction. TDI-based polyurethane, on the other hand, may be more prone to degradation over time, leading to a shorter lifespan for products. However, advancements in recycling technologies have made it possible to recycle both MDI and TDI-based polyurethane, reducing their environmental impact.


MDI and TDI find applications in various industries due to their unique attributes. MDI is commonly used in the production of rigid foams, such as insulation materials for buildings and appliances. Its excellent mechanical properties and resistance to heat make it suitable for these applications. TDI, on the other hand, is often used in the production of flexible foams, such as mattresses, cushions, and upholstery. Its good flexibility and resilience provide comfort and support in these applications. Both MDI and TDI are also utilized in coatings, adhesives, sealants, and elastomers, each offering specific advantages based on their properties.


In conclusion, MDI and TDI are two important isocyanates used in the production of polyurethane. While they share similarities in their purpose, their chemical structures, reactivity, physical properties, toxicity, and environmental impact differ significantly. MDI offers excellent stability, mechanical strength, and durability, making it suitable for applications that require high-performance materials. TDI, on the other hand, provides good flexibility and resilience, making it ideal for applications that require cushioning and comfort. Understanding the attributes of MDI and TDI is crucial in selecting the appropriate isocyanate for specific applications, ensuring optimal performance and safety.

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