Is All Resin Flammable?

The word “resin” is an umbrella term for all sorts of mixtures of chemicals. For example, it could mean epoxy resin, which is used in both art and DIY. But it could also refer to polyester or casting resin. These differ completely from epoxy resin and have a different chemical composition.

It’s important to know what resin you’re dealing with before you start using it, as each type comes with its own risks and dangers. Therefore, some can be flammable while others are not.

Is All Resin Flammable

Epoxy Resin

While epoxy is an inherently flammable polymer, it requires an extreme temperature to do so. If you follow all the correct safety precautions, then there’ll be no risk at all of your epoxy resin catching fire. 

When you purchase epoxy resin, it’ll come in 2 parts; resin and hardener. When resin and hardener are mixed together, the mixture heats up, which is what causes the mixture to harden.

But, if the mixed resin and hardener combination gets too hot, it can melt the mixing cup or catch the cup on fire. That fire can then spread to your work area and get out of hand quickly. 

As a result, whenever professionals are working with epoxy resin, they'll usually have a metal container and a fire extinguisher nearby. This means that if their resin overheats, they may quickly transfer the mixing cup to a non-flammable container.

 If you use resin for a long enough period of time, you will most likely encounter a circumstance in which your resin becomes hot and begins to smoke. It is critical to plan what to do if something occurs in order to avoid injury.

How to stop epoxy from catching fire

Be careful of the total volume of resin and hardener that can be mixed at the same time. More than this amount will result in overheating, which may cause the epoxy resin to catch fire in the mixing cup. Before you begin, always read the directions on the bottle.

Understand that the thicker the layer of resin you pour, the faster heat will build up. While the heated resin is unlikely to catch fire in your mold or on your surface, it may cause it to melt, causing a large mess.

Heating your resin kit in a water bath is an excellent way to quickly allow bubbles to leave the mixed resin. 

However, keep in mind that this heat contributes to the overall heat of the process. If your resin components are heated, the resin reaction may be accelerated to the point that your mixing cup catches fire.

What about cured epoxy resin?

Once the resin and hardener mixture has set and is completely solid, it is “cured.” Cured epoxy resin is not flammable. However, it’s not heat resistant either, unless you specifically purchase the heatproof kind.

If exposed to an open flame, cured epoxy could melt or become burned, but it won’t set alight. People still use resin to craft ashtrays that come into contact with hot ash and open flames all the time, it would need to come into contact with another accelerant in order to catch on fire.

Is Polyester Resin flammable?

Polyester resins are synthetic resins that are created through the interaction of dibasic organic acids with polyhydric alcohols.

Unsaturated polyester resins are found in sheet molding compounds, bulk molding compounds, and laser printer toners. Most polyester resins are viscous, pale-colored liquids made up of a polyester solution in a reactive diluent.

Polyester resin is considered flammable, much more so than epoxy resin. This is why many people opt for modern 2-part epoxy resins rather than the polyester kind.

Polyester resin has a flashpoint of just 66 degrees Fahrenheit (or 35 degrees Celsius). This is very low and easily reached, so a tiny spark or small flame could result in a polyester resin fire.

The dangers of polyester resin

As well as being flammable, there are many other reasons why you may want to avoid working with polyester resin. For example, the catalyst in a polyester resin reaction is Methyl Ethyl Ketone Peroxide (or MEKP, for short). 

MEKP is a particularly nasty substance and is indeed flammable. It’ll burn any surface it lands on, your skin, your eyes, and other sensitive areas such as under your fingernails, and it really burns.

This “burn” is a chemical reaction that is taking place beneath the layers of your skin. It doesn’t feel good, because it isn’t. 

As well as this, the dust and fumes caused by MEKP is just as harmful. You should never use it without a respirator mask and other precautions in place.

You should also only work in a well-ventilated space where you, other people, children, and pets won’t be affected by the fumes. Polyester resins give off styrene monomer.

This monomer is toxic and inhaling it can cause dizziness and sickness at low concentrations, and at high concentrations can be fatal.

Dermatitis can be caused by polyester resins. This is most likely because the styrene dissolves the skin's natural protecting oil. Individual susceptibility differs from person to person and scenario to scenario.  

When working with polyester resin, avoid letting the resin come into contact with the operators' hands, and careful use of barrier cream before beginning work and skin washing cream afterward gives enough protection.

If there’s any chance of the resin coming into contact with your eyes, always wear goggles or sufficient eye protection.

Any cloth, absorbent paper, or other material used to mop up resin spills poses a fire risk due to the possibility of heat and spontaneous combustion, especially if the resin was catalyzed.

Amounts of catalyzed resin of more than 0.1 kilos can also generate harmful exothermic heat if allowed to polymerize in a mass. All soiled or trash materials must be soaked in water and stored in a closed bin until they are disposed of.

Small amounts of resin and resin-contaminated waste can be disposed of safely by burning it in an approved incinerator that does not generate smoke or sparks and is located in a secure location.

A garbage collection contractor is usually in charge of disposing of larger amounts of waste.

Is casting resin flammable?

Casting resin is just a different name for a specific type of polyester resin, so yes, it is flammable. You’ll need to take the same precautions with casting resin as you would with Polyester resin (see above).  It’s often used for making models, busts, and prototypes. 

A few grades of polyester casting resin also contain a methyl methacrylate monomer. These grades of polymer casting resin will have the warning “Highly Flammable” printed on the label.

The advice covers both types of resin. There are some resins that contain no monomer at all and these are often called “solvent-free” resins. Solvent-free resins won’t have a fire hazard warning on the label. 

Conclusion

While we’ve established that “resin” can mean a lot of different things, as a rule of thumb, it’s safest to keep any resin away from extreme heat and open flames.

While the risks associated with epoxy resin are minimal, extra precautions should be taken when working with polyester or casting resins.