Epoxies are thermoset polymers used for their excellent adhesive properties, high tensile and compressive strength, and chemical and thermal stability. Learn more about it here.
Kim
Published Date: 2026/1/7
Epoxies are thermoset polymers that are really like chameleons in their ability to change and adapt depending on what they’re needed for. They can be used to coat and seal a floor or structure, painted between two components to serve as an adhesive, and found among the bottles of glue in craft kits. This adaptability hints at their top-notch characteristics and why people often reach for epoxy in many situations. They’re great adhesives and have a higher tensile and compressive strength — not to mention they remain chemically and thermally stable in a variety of environments.
The science behind epoxy is fascinating. In plain sight, you’ll see that it can turn from a liquid or paste into a solid. Under the microscope, you’ll notice that this occurs through a series of cross-linking that happens between groups of epoxides and hydroxyl that are already within the pre-polymerization resin.
To get this reaction to take place, you’ll either use two chemical agents that’ll cause the coupling and free radicals to appear or you’ll use a catalytic hardener that’ll trigger this response. Either way, once this reaction happens, it’ll result in a strong, hardened surface. 
Epoxy has been around for a while, but more recently it has played a large part in 3D printing, including in our own 3D printing services here at Fsproto. It has more than one purpose, too, and below we’ve broken down all the ways in which this material can be used:
Swiss chemist Pierre Castan can be thanked for creating epoxy resin after experimenting with reactions between several different chemicals. This happened in the 1930s and he was eventually granted a patent in 1940. Around the same time, a German chemist named Paul Schlack was also toying with different materials, leading to the ability we now have to synthesize and manufacture epoxies.
In the 1940s and 1950s, the dental industry started using epoxy and gradually it began gaining traction in other industries, like the aerospace, marine, and automotive sectors. Twenty years later, they entered the consumer market and have since remained an important material for large manufacturers and companies as well as individual hobbyists.
Looks-wise, epoxy morphs from a paste, liquid, or gel into a hardened solid. It’s usually clear or slightly opaque and you can tint it in numerous different colors. Outside of its appearance, it has many mechanical and physical properties that make it a favorite adhesive and coating.
Epoxy not only has many useful properties, but it comes in a long list of different types, which is useful for customizing the epoxy for your intended application.
This is the closest formula to the original epoxy that appeared back in the 1930s. However, they’ve been tweaked and reformulated to have even higher strength and resilience as well as faster curing times. This is a great cost-effective option for a wide range of purposes, such as for repairs and furniture making.
This type of epoxy isn’t truly water-based as it’s often called, but it has a water-dispersed composition that will evaporate when it’s cured. It’s a smart formulation to use when you’re sealing tanks or in need of a waterproof sealing agent. They also have low to no volatile organic compounds, which makes them a safe choice when you’re applying them in enclosed environments around people.
As the name implies, this type of epoxy is cured through a UV light and is a two-part process. The epoxy and the chemical that will initiate the reaction are both applied and then hardened through UV. You’ll commonly see this in casting, artwork, and even dental work. Because the epoxy can be irritating or relatively toxic, it takes a well-trained professional to apply it. UV-sensitive epoxy resins are also common in the material used for certain additive manufacturing processes that we offer.
Structural epoxies are perfect for applications that require bonding difficult materials or items or structures that will need to be machined after. This type of epoxy doesn’t slump and it’s pretty viscous, so it’s well suited for filling in gaps and serving as an electrical insulator. They’re also resistant to abrasion, water, and impact, making them an all-out great choice.
For applications where you’ll be subjecting surfaces, structures, or objects to extremely high temperatures, this is the best-suited epoxy for the job. They have very similar properties to other epoxy resins but can withstand temperatures up to 300° C and have good chemical resistance too. They’re typically made with a bisphenol F diglycidyl ether copolymer that gets cured through a fatty acid or tetraethylenepentamine polyamide.
Within the makeup of flexible epoxies are rubber or elastomer beads that give extra shock tolerance, toughness, and flexibility to the final hardened product. There have been important breakthroughs recently with this type, thanks to the silane and siloxane components within the epoxy. Mixed into the formula, they provide a cross-linked material that’s tough when cured but still ranks as a 20D on the Shore Hardness scale, which is softer than a rubber heel of a shoe.
A conductive epoxy helps support electrically conductive environments (though they aren’t intrinsically conductive), while also offering surfaces or sections of parts an anti-static, flexible, and durable coating or composite. You’ll find them in repair pastes for etched copper tracks, wristbands on fitness tracking equipment, and circuit boards.
On top of epoxy types, there are also specific classes that speak to the chemical groups that make up each type, which we break down below.
This class of epoxies has a functional glycidyl group within their chemical structure, and the resins form through the reaction between epichlorohydrin and a reactive hydrogen compound, like bisphenol A (BPA). From it, you get an epoxy with a linear and branched makeup that has great thermal and chemical resistance and top-notch adhesion. Manufacturers and companies looking for quality adhesives and coatings or an epoxy that works on electronics products or composite materials will likely opt for one of these epoxies.
This epoxy involves the chemical reaction between phenolic novolac and epichlorohydrin. In comparison to a glycidyl epoxy, or one with BPA in its structure, it offers more chemical resistance and thermal stability thanks to its highly cross-linked structure. This epoxy is usually cured with amines and often has toxic substances in its makeup (like formaldehyde and phenol), so they should be used carefully and in the right environments.
The chemical structure of these epoxies features a ring-like structure as their backbone, making them more rigid and compact. They’re often found in the manufacturing of composites, coatings, and adhesives and usually contain hazardous substances, so it’s best to take care when you’re working with this type. They’re reliable for instances where chemical resistance, mechanical strength, and electrical insulation are important.
Similar sounding to cycloaliphatic epoxies, these differ in that they don’t have a circular structure within their makeup, but a straight or branched set of carbon chains instead. This makes them less rigid than their cyclo-counterparts, lending themselves to situations where flexibility is key. These epoxies are also very useful if you’re after UV resistance, color stability, and low toxicity. That’s why they’re often found in marine, automotive, outdoor, and food applications.
An aromatic epoxy also features a “ring” within its chemical structure and is a product of BPA and epichlorohydrin reacting together. They’re great epoxies for lining containers and tanks as they have high levels of chemical resistance and are strong and stiff. They’re relatively glossy as a finish but they’re not ideal for applications that need to retain their color. It’s another class of epoxies that should be used with caution as they contain hazardous substances, too.
This class includes epoxies that mix two or more types. As an example, this could be a blend of a cycloaliphatic epoxy with a novolac epoxy. Hybrid epoxies are created and used when you need specific benefits that only occur when you combine several together, and it leads to a material that can be used as a coating, adhesive, or composite in industries that require a higher level of performance, like the aerospace, construction, or automotive sectors.
There are a few important considerations to keep in mind when you’re selecting an epoxy. The most important priority is choosing a type or class that’s fit for the application you have in mind. It should be formulated for adhesion, coating, or creating a composite material. Epoxies are also made for specific materials, which ensures that it’ll create a secure and durable bond for that specific surface. There are also a range of cure times, which may be important to note depending on the timeframe or outlying factors that can affect a successful epoxy coating.
In harsh environments or those exposed to high temperatures, choose an epoxy that’s built to handle these factors for the best results. Epoxies can also lead to health problems and hazards (like fires), so check warning labels, find the right environment conditions, and wear the right safety equipment.
As a general guideline, two-part epoxies give the best results in metal bonding. The choice of which types of epoxy resin depend on the details of the application. Choose an epoxy that has the appropriate properties for the application and is developed for bonding metal surfaces. Some tips are listed below:
There are many types of epoxy resins available that ostensibly bond well with plastics. However, it is important to take into account the nature of plastic. Listed below are some guidelines to follow:
It's beneficial to choose an epoxy that is specifically designed for bonding plastics, as this will probably achieve a stronger overall bond.
For bonding cement, various epoxies can give good results and are listed below:
The type of epoxy best for polymers are plastic bonding agents, fast-setting epoxies, flexible epoxies, and structural epoxies.
Read on to get a small snippet of the long list of applications there are for epoxy:
When working with epoxy, it’s good to have an idea of the pros and cons that come with this material. Some of the advantages include that epoxy:
There are also a few disadvantages to note. Epoxy can:
Epoxies offer a wide spectrum of cure times—from minutes up to several days (for full strength). Often the cure time is closely related to the bond quality and overall material strength/toughness, so the trade-off in cure convenience can come at a cost.
For rigid epoxies, the material will generally be fully cured when it loses all indentability when pressed with a point or edge. In most cases, part-cured epoxies will dent with a fingernail. When they harden, they are generally at full strength. For flexible epoxies, this may not apply and manufacturers' curing schedules should be considered. Some epoxies require a very prolonged cure time to achieve full strength, so refer to the maker's recommendations to evaluate cure completion. Cure time can be accelerated with a slightly elevated temperature, but it is important not to exceed the maximum service temperature.
Epoxies have an unlimited functional life span provided that they are not exposed to attack from conditions that are outside their recommended limits. This includes: excess heat, radiation, UV, aggressive solvents, or excess stress.
Yes, epoxy breaks easily. Most basic epoxies are strong materials but they are brittle and cannot handle deflection well. This leads to easy breakage when general epoxies are used to bond more flexible components. Toughened and flexible epoxies go a long way toward reducing this vulnerability.
Some alternatives to epoxy are listed below: