Why Heat Matters in Resin Printing - Yes, That's 3D Printed

Why Heat Matters in Resin Printing

If someone told you to warm up your resin printer, you might be wondering why that would ever be necessary.

After all, we print with light, not heat, right?


Below we write about why the cold might lead to your prints failing, and how you can strengthen them by adding heat.

I. What’s happening inside the resin

Is heat necessary for resin printing?

You might already know that photopolymerisation (the chemical reaction used in stereolithography) requires light to solidify the resin, not heat.

While that is true, temperature does play an important part in making the resin more reactive, and makes it require less energy to be cured.

This is believed to be because heat gives the particles energy. It makes them wiggle more and wiggle faster. This gives them a better chance to meet and interact with each other.

It is sort of how sugar dissolves easier in hot water. The water molecules are moving faster, and spread further apart, leaving more space for the sugar to fit between them.

Okay, but what does that mean for me?

To put it very simply:

hot resin = more reactive
cold resin = less reactive

Most resins perform best above 25°C, and will begin to fail below 20°C.

Let's see the implications of this.

Printing in hot and cold environments

Temperature effectively changes the critical energy (Ec) required to cure the resin.

For practical purposes, this means that your exposure time for any given resin will increase or decrease depending on the weather.

Let's take an exaggerated example:

Your room temperature in spring is 22°C, and you print Acme Resin perfectly with an exposure time of 3s per layer.

The summer comes, and your room temperature increases to 30°C. Suddenly all of your prints are overcured. You now have to lower your exposure time for Acme Resin to 2.5s to print accurately.

In autumn the temperature drops, and you have to switch back to 3s exposure time.

Then winter comes, and all of your prints start failing, no matter how long the exposure time is. You furiously re-level your build plate every day, and mutter curses at the people who sold you the printer.

II. What's happening inside the printer

The plot (and resin) thickens

So why doesn't a longer exposure time work at very low temperatures?

The energy required to cure the resin is one thing, but there are other forces at play on a mechanical level.

Temperature changes the resin’s viscosity. The colder it is, the thicker it gets, the warmer it is, the more liquid and runny it becomes.

hot resin = less viscous
cold resin = more viscous

Resin that flows better is easier to print.

Let’s see why:

After every layer, the build plate separates from the FEP, and leaves a gap in its own place. The resin needs to flow back into that gap before the new layer can start.

This is the why resting time exists. If your resin flows easier, your resting time can be quicker.

Then the build plate needs to move back down, leaving a layer of resin of just 50 microns, or however much your layer height is. If the resin is more viscous, it is harder to push down, and might again require more resting time.

 You can of course be a daredevil and forego these resting times, but this may result in strange artefacts on your print, caused by the resin curing while it’s still flowing.

You can see an example of this here:

Photo source: Ameralabs

Can I just print with less viscous resins?


But you should be aware of what that means.

When a resin is more viscous, it is usually to achieve a desired property.

For instance, 8K resins contain more light blockers / pigments to bring out smaller details in models.

Engineering resins contain larger molecules and additives that make them tougher, more heat resistant, or give them some other beneficial properties.

There is actually a new industrial segment focusing on printing extremely viscous resins, because they offer better properties. It is called hot lithography, and ⁠— as you might have guessed ⁠— requires a lot of heating.

There are now even resins that are shipped completely solid, and must be melted before printing.

So yes, you can use less viscous resins to make printing easier, but your prints will likely be more brittle and fragile coming out.

Don’t play with the thermostat!

To be more precise, it is not enough to just heat the printer arbitrarily. In order to have consistently good prints, you have to maintain an optimal temperature.

Just imagine, if one layer is cured at 20°C, and the next one is cured at 30°C, you will likely see some visible difference between the two, and you could even see parts failing completely.

Here's a picture of a print where the temperature kept changing every few layers:

Photo source: A Blog in Miniature

This sudden temperature change can actually happen very easily.

Here are some common culprits, and how to avoid them:

  1. Do not open your printer / enclosure during printing if the room temperature is significantly different from the temperature inside.

  2. Do not pour cold resin inside the printer half-way through. If you need to top up, heat the new resin to your desired temperature first.

  3. If you are using an external heater, make sure it is one that is designed to maintain a constant temperature. More on this below.

  4. If you heat up your resin before printing (eg. in a bath), make sure that it maintains its temperature for the entire duration of the print. More on this below.

III. 7 methods to heat your resin printer

1. Use a printer with a thermostatic heater

This is the simple, professional option that will always yield consistent results.

It is also the reason why we are writing this article.

Our hero product, the UniFormation GKTwo, was designed with a built-in thermostatic heater, which keeps the print temperature at an optimal 26°C at all times.

Check it out:

If you are having trouble with your prints due to the cold weather, the GKTwo can be a quick solution to all of your problems.

There are many other reasons why the GKTwo is the best 8K printer you can buy right now, but… We don’t have time to discuss those here.

UniFormation GKtwo | 8K LCD Resin 3D Printer with Built-In Heater


2. Warm up the room you are printing in

Perhaps it sounds obvious, but we need to mention it.

Especially if you’re printing at home, simply increasing the ambient room temperature is the easiest way to deal with the cold.

You have to take into consideration however that you will need to be heating an entire room instead of just a small enclosure. This can be more or less expensive depending on energy prices.

3. Use an enclosure

Phopolymerisation is an exothermic reaction, meaning that excess heat is generated during the printing process. An enclosure can help you capture all this heat, as well as any other heat the machine generates.

That means that as long as you can start the first few layers successfully, you might just get lucky, and have the resin carry you the rest of the way itself.

If you don’t have an enclosure yet, you can

  • buy one — there are some fairly cheap options
  • build one for yourself
  • put your resin printer in an unused closet
  • put a cardboard box over your printer (see here at 2:00)

Example of a grow tent as an enclosure. Photo source: Reddit

You should always monitor the temperature inside the enclosure to make sure it gets to, and stays above 25°C.

Another benefit of enclosures is that they also trap some of the unpleasant fumes that the printer releases.

(Which reminds us, the UniFormation GKTwo comes with a carbon air filter that captures fumes even without an enclosure.) 

Why this is not a great option by itself

As we said before, the print at least needs to get started before the exothermic heat is generated. That means you might have to employ some other heating method to get the print started.

The printer can only generate so much heat by itself. If the temperature outside is especially cold, this heat might very well not be sufficient.

4. Warm up the resin bottle before pouring it into the printer.

You can warm up the resin while it is still in the bottle, and pour it into the printer that way.

Most people use a warm water bath to do this, you can see an example of it here at 1:00.

This is a safe and easy option, just make sure no water can leak inside the bottle. It doesn’t need to be fully submerged.

Photo source: WikiHow

You can also use a heater directly on the bottle, or use an industrial oven. (Do NOT use your kitchen oven, as this will almost definitely end in a catastrophe.)

Why this is not a great option by itself

Heating the resin before printing only works if you are then able to maintain that temperature for the entire duration of the print.

Otherwise, as the resin cools inside the printer, your first few layers will require significantly different exposure times than your last ones. This could result in your prints starting out well in the beginning, but failing towards the end.

Moreover, if you have any leftover resin in the vat, you would have to put it back in the bottle to use it again, or find some other method of heating it.

💡  Using an enclosure together with a warm bath can make this technique much more effective.

5. Place a heater next to the printer or inside the printer

This is the same type of heater that you would use to warm up a room in the winter.

These heaters are fairly inexpensive, and running them also doesn’t cost as much as you might think, especially the smaller ones.

Placing heater inside the printer is usually the better option, though some smaller printers also lack the necessary space to place the heater inside.

Check online (eg. in Facebook groups) to see if anyone has successfully installed a heater for your type of printer. Sometimes you need some extra setup to help mount the heater, and they might be able to help you with it.

There are three types of heaters you can use:

  1. Always on. The kind that keeps going until you turn it off. This can lead to temperatures which are too high.
  2. On/off thermostat. This heater will turn off once your desired temperature is reached, and will only turn on again if it detects a temperature that is eg. 1°C below your setting. This change back and forth can lead to visible layer lines. ref
  3. Proportional thermostat. This heater doesn’t turn off, but adjusts its heating power automatically based on the air temperature it measures. It is the best option for consistent prints.
If you are using a heater next to the printer, make sure you keep it well clear of flammable materials such as IPA!
💡  Using an enclosure together with a heater can make this technique much more effective.

6. Attach heat mats to the printer

If you ever owned an iguana, you might be familiar with heat mats.

They are mats or pads that transfers heat directly to the object they are in contact with.

They are normally used in vivariums, but some clever makers started attaching them to the outside of their printers to warm them up. Alternatively you can place one under your printer to stand on.

Unfortunately we don’t have any data about how these compare to a regular heater. They are likely very similar in effectiveness.

7. Wrap a fermentation belt around your vat

This is probably our favourite.

Fermentation belts are silicone belts that have a heating wire running inside. They are traditionally used to make beer through fermentation.

Some people wrap these around their vat to keep it warm. You can see an example here at 2:54.

Heating the vat directly is likely a better option than heating the chamber, as it is more likely that the resin will actually take on your desired temperature, as opposed to just the air being heated around it.

If you are already using one of these belts to make beer, please don’t stop making beer! Just buy another belt.


IV. Bonus content

Bonus: How to store your resins

Taking our formula of cold resin = less reactive also explains why you should store your resins in a “cool dry place”.

It will make them less prone to accidental reactions inside the bottle, and will degrade slower.

Bonus: Adding heat during post-curing

We can also take our formula of hot resin = more reactive, and apply it to the post-curing process.

After the resin is cured, there are still some floating molecules inside that can bond with each other in the presence of light. This is why we do post-curing.

By increasing the temperature of the print, we are giving energy to the molecules to float around more and faster, which will give them a better chance to bump into each other, and bond.

Therefore, heating the print during the post-curing process will result in faster curing, and also stronger mechanical properties by as much as 50%.

Formlabs for instance recommends various post-curing temperatures for their resins, up to 60°C. It is possible that above these temperatures, prints would start to deform, or we would just get diminishing returns.

Bonus: Maximum layer height affected by temperature

Interestingly, the maximum layer height you can achieve is also affected by the viscosity of the resin. The runnier it is, the easier it lets light through, and lets you print with bigger layers.

This is why 8K resins usually say that you shouldn’t print them at a layer height bigger than 100 microns. They’re very thick, and block the light from traveling through.

This can also be helped by heating the resin, although only up to a point.

It is also worth noting that for the same reason, overheating average resins to 40°C or more can cause light bleed and scattering. This means resin will be cured in places where you wouldn’t want it to.

Maintaining an optimal temperature between 25-30°C is usually best for commercial grade resins.

V. References

Thank you for reading.

This article draws heavily on the references below, and could not have been possible without them. Thank you to everyone who is trying to make our printing life easier through research.

We would also like to send a special thank you to Honza Mrázek, who regularly publishes original research and findings on his blog, moving our collective konwledge forward.

If you think something should be added or corrected, please let me know at adam@yesthats3dprinted.com. We try to provide the most accurate information possible, but we do make mistakes sometimes.


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