What is the difference between epoxy and polyester?

The differences between epoxy and polyester are important to know if you are considering working with these materials. In this article, we will discuss the main properties and applications of both materials. That way, you will know exactly which material is most suitable for your project and you will be able to get started with peace of mind.

Do you have any questions about epoxy or polyester? If so, feel free to contact our expert support team!

What are epoxy and polyester?

Epoxy and polyester are both synthetic resins, meaning they are composed of synthetic materials. Both epoxy and polyester consist of two components: a base (component A) and a hardener (component B). When you mix the two components together, a chemical reaction occurs that releases heat. This forms a hard, strong and durable compound. Synthetic resins such as epoxy and polyester are popular in (boat) building, industry and among do-it-yourselfers because of their versatility, strength and durability. Although they may look very similar at first glance, there are some important differences between epoxy and polyester.

Properties of epoxy

Epoxy is a very strong and durable material known for its excellent adhesion to almost all substrates. It is resistant to chemicals and water and boasts high mechanical resistance. Thanks to its UV stabiliser, epoxy is also suitable for outdoor applications. Moreover, epoxy is highly dimensionally stable, meaning it does not shrink during curing. This makes it ideal for repairing cracks and holes, coating floors and bonding different materials. Epoxy is also popular with hobbyists for making jewellery, coasters, artwork and repairing objects.

Properties of polyester

Polyester is a cheaper alternative to epoxy and is often used for larger projects where cost is an important consideration. It is often used to make glass fibre reinforced plastic (GRP) objects, such as boats, car parts and swimming pools. Polyester resin is also suitable for making moulds and casting objects.

When do you choose epoxy and when polyester?

Now that you know what epoxy and polyester are, it is time to discuss the main differences between these two materials. Here, we will look at the adhesion, UV resistance, waterproofing, chemical resistance, shrinkage, processing (smell) and price of both materials.

  • Adhesion: if you are looking for a material with excellent adhesion to almost all substrates, epoxy is the best choice. In fact, epoxy adheres effortlessly to steel, aluminium, concrete, wood, stone, polyester and more materials. Polyester generally does not adhere as well and can come off if not prepared properly. So for epoxy, you generally need less preparation.

  • UV resistance: are you going to make something where the final coat will be applied outdoors and exposed to sunlight? Then polyester is the best choice. Polyester resin actually has better UV resistance than epoxy resin. This means that polyester is less likely to discolour or yellow under the influence of sunlight. To counteract yellowing of epoxy, you can choose to use a UV-stabiliser. This significantly increases the UV stability of epoxy. At Polyestershoppen, you can also find high-tech epoxy systems with a built-in UV filter, such as RESION UV Epoxy and RESION Epoxy for large castings.

  • Watertightness: epoxy is water and vapour tight. Polyester, on the other hand, is only waterproof when finished with a gelcoat or epoxy system.

  • Chemical resistance: epoxy resin is more resistant to chemicals, such as acids, bases and solvents. This makes epoxy extremely suitable for applications where the material comes into contact with aggressive substances (such as in the chemical industry) or when protecting concrete floors from chemicals. Also, epoxy's mechanical resistance is 3 to 4 times stronger than polyester.

  • Shrinkage: if you want a tight finish without shrinkage cracks, epoxy is the right choice. Polyester can shrink up to about 5% during curing. This can lead to a less attractive result.

  • Processing (odour): unlike polyester, epoxy resin hardly gives off any odour during processing. Processing epoxy therefore does not require a fume mask and you can work indoors (if you can ventilate the room properly). Are you going to work with polyester? Then work outdoors or in a very well ventilated area. Moreover, always use a suitable fume mask. In short, polyester stinks, epoxy does not.    

  • Price: an important difference between epoxy and polyester is the price. Polyester is generally cheaper than epoxy. Do you have a limited budget or are you undertaking a large project? Then polyester may be a more economical option.

As you can see, both materials have advantages and disadvantages. Therefore, the choice between epoxy and polyester often depends on your specific project and needs. It is important to carefully consider which properties are most important for your application. We would be happy to help you make this choice. Please feel free to contact our specialists.

Conclusion: epoxy or polyester?

The differences between epoxy and polyester are mainly in the properties of the materials, such as adhesion, chemical resistance, UV resistance, shrinkage and cost. Epoxy is a stronger and more durable material better suited to applications where good adhesion, watertightness and chemical resistance are important. Polyester is a cheaper and more flexible material suitable for larger projects and applications where cost is an important consideration. By comparing the properties and applications of both materials, you can make the right choice for your project.

We have once again listed the properties of epoxy and polyester for you:

Epoxy properties Polyester properties
Adhesion to many materials Frequent pre-treatment required
UV-resistant by adding stabilisers High UV resistance
Waterproof Not waterproof
High chemical resistance Less resistant to chemicals
Odourless (solvent-free)  Strong odour
Hardly shrinks  Can shrink up to approx. 5%
More expensive Cheaper

Need more information on epoxy or polyester?

Do you still have questions about epoxy or polyester after reading this article? Then feel free to contact our expert supportteam. We are more than happy to offer free, non-obligation advice! 

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