Polyurethane And Silicone Sealants: Key Differences

Polyurethane and silicone sealants are two of the most commonly used sealants and are considered elastomeric material that is used to fill in openings, gaps, and cracks that prevent air and water from seeping into them. As compared to other sealants like acrylic, they are also similar in the fact that they are relatively flexible and easier and have an allowance of 50% movement. While they behave similarly in these aspects, they are also very different due to the different properties that make them unique and suitable for specific applications. So what are the key differences? Read on to learn more about polyurethane sealants vs. silicone sealants.

Chemical Properties And Shell Life

One of the biggest differences between polyurethane and silicone sealants is their chemical makeup. Polyurethane sealants are made from organic, natural materials, comprising polymers made with diisocyanate and polyol joined by carbamate. On the other hand, silicone sealants are made with inorganic material composed of synthetic polymers forming the dominant chain of polysiloxane, which joins together oxygen and silicon atoms.

Chemically, their lifespan is also affected by the environment they are exposed to, such as UV light, with organic materials being more reactive to it than inorganic materials over time. This causes their properties to change significantly, which will reduce their lifetime in being an effective sealant.

Shelf Life

Generally, most polyurethane sealants have a lifetime ranging from five to ten years. In general, silicone sealants will last at least 20 years and come with warranties from manufacturers that offer you their guarantee if your sealant has worn out faster than the expected shelf life. This is partly due to their distinct chemical properties, which makes silicone sealants last longer than their organic counterpart – polyurethane sealants. Other variable factors that will impact the lifetime include weather conditions, environment, wear and tear, and the amount of exposure to UV rays.


You get what you pay for with these sealants. As silicone sealants generally last twice the lifetime of polyurethane sealants, they also will cost twice as much. This cost includes both the initial cost of the product as well as the amount of labor needed to be factored in when installing the sealant. While polyurethane sealants are generally more affordable, you will have to caulk at least twice to match the lifetime of a silicone sealant. On the other hand, while you will only need to caulk once during its lifetime, you will have to pay more. Depending on your preference, these two sealants may cancel each other out when It comes to costs.

Transitioning from Silicone to Polyurethane Sealant

A good rule of thumb is never to mix the two sealants. If you wish to re-caulk a surface that was previously sealed by polyurethane, then you will have to ensure that any remaining material is removed to protect the integrity and durability of the silicone sealant. Also, mixing the two is never a good idea as this can cause the other type of sealant to deteriorate and degrade more quickly than usual, rendering the seal ineffective. In many cases, it would be more cost-effective to take the time and get the caulking job done right the first time, instead of replacing an old or railed sealant.