How To Cure UV Resin Without UV Light: Is It Possible?

Resin 3D printers are undeniably the technology of the future. Their main advantage is print accuracy and object smoothness compared to FDM printers. When it comes to choosing the print material, you can opt for standard, 2-part resin or the popular UV resin. If you go for the latter, you must also invest in an appropriate UV resin curing light

In fact, you cannot cure UV resin without UV light. Unlike 2-part resin, UV resin doesn’t have a hardener. Instead, the photons in the UV radiation trigger a chemical reaction that causes the resin molecules to bind together and form a network. This reaction causes the resin to harden.

Do You Need UV Light For UV Resin?

In short, yes. All UV resin requires UV light for curing. You don’t necessarily have to buy a UV lamp, though. Sunlight exposure can also do the trick, although it may take more time for your object to harden.

For this reason, we recommend using a professional UV curing machine. This device can cure UV resin in minutes, minimizing the risks of damage; however, not all UV lamps were created equal, and the one you use can make or break the deal.

UV Resin vs. Regular Resin

There are several ways of using resin in 3D printing, but in the end, it all comes down to the type of resin you use. There are two resin types: UV (or 1-part) resin and regular, epoxy resin. Each type comes with advantages and drawbacks, so let’s see which one to pick for your project.

UV Resins Known As 1-Part Resins

UV resins are polymerized materials that can be cured with energy from UV radiation in a very short amount of time. Depending on the layer thickness, this resin type cures within seconds or minutes once exposed to UV light, but it remains manageable (it doesn’t cure) without UV exposure. 

This comes as an advantage, increasing the processing time and allowing you to print more intricate objects.

Another huge advantage is that you can use UV resin as it is. This resin type requires no messy mixing or ratio calculation if you don’t want to use the whole tub.

The main disadvantage is that the UV resin layer has to be fairly thin to allow for proper curing. If you’re printing objects thicker than 3mm, you should work in layers and cure each layer before printing the next layer. This process could be tedious. 

Another slight drawback is that you need a special lamp to cure the material. While most UV resin cures when exposed to sunlight, this doesn’t work optimally in most cases.

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Types of UV Resins That Need UV Light to Cure

There are various types of UV resins you can work with, including: 

  • Polyester resins: Not all polyester resins cure with UV light, but the UV solar cure polyester resin type is an excellent choice for beginners who don’t want to invest in a UV lamp just yet. This resin contains a catalyst that activates when exposed to natural UV rays or bulbs and cures in about three minutes. Solar exposure works beautifully for curing, but only if you live in a warm climate area that gets plenty of sunshine.
  • Polyurethane resin: Synthetized from polyester polyol, UV polyurethane resins are a perfect choice for printing more delicate components. Polyurethane resin needs at least 250 nm to cure, but the end result is incredibly scratch- and stain-resistant. 

Non-UV Resins Known As 2-Part Resins

Two-part resins (regular resin), as their name suggests, comprise two components that harden when mixed together. These resins don’t need UV light to cure since the catalyst will harden on its own. However, the curing time is longer compared to UV resin.

The secret to working with non-UV resin is respecting the predefined mix ratios when preparing the product, especially if you want to reduce the quantity of resin you prepare. Using too much or too little hardener can have disastrous results. 

Non-UV resins have longer shelf life compared to UV resins, but you can’t use the leftover product after you’ve mixed it (the product will likely harden). These resins are also less expensive, but they can become brittle and crack in time.

Types of Resins That Don’t Need UV Light to Cure

Most 2-part resins on the market are epoxy resins that must be properly mixed before you can use them. Epoxy resins don’t need UV light or special environmental conditions to cure, although they might cure faster in a warmer temperature.

UV exposure has no effect on this resin type, meaning that you cannot cure the epoxy resin with UV light. Epoxy resin is mostly used with the hot-lithography stereolithography 3D printing technology, whereas you can print UV resins either with stereolithography (SLA) or digital light processing (DLP) 3D printing.

Choosing UV Light Options To Cure Resin

Curing UV resin isn’t complicated, but you must use a UV lamp or torch that is big enough for your object. You should also pay attention to the bulb’s power, ensuring it has the right light intensity for your project. With this in mind, let’s see how to cure UV resin.

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1. Sunlight

Direct sunlight is generally enough to cure UV resin; however, this option is not always optimal. You need strong sunlight for the purpose, so the resin might not cure on a cloudy day no matter how long you wait. Curing in sunlight also takes a lot of time, and the slow hardening process might have a negative impact on the final result.

Time to Cure

UV resin can take anywhere between 20 minutes and a few hours to cure in direct sunlight. The actual time depends on the amount of sunlight.

2. LED Flashlight

UV LED flashlights are an excellent alternative to sunlight. Cheaper than UV lamps and easy to use, they are a great choice for smaller objects. When choosing the flashlight, it is essential to check the LED bulb’s wavelength and its power.

How Many Watts To Cure UV Resin?

The easiest way to determine how many watts you need to cure UV resin is to check the manufacturer’s specifications. Each resin comes with indications regarding the bulb power and wavelength range required. 

As a rule of thumb, the flashlight should have at least 4 watts and a wavelength range between 356 nm to 400 nm. You may be able to cure some polyurethane resins with a weaker bulb (about 250 nm wavelength), but you might have to wait longer.

Regardless of the flashlight power and wavelength, you should always wear protective equipment when using the UV flashlight, including eye protection and a facemask with a respirator.

Keep in mind that UV light can produce irreversible eye damage. At the same time, UV resins could release toxic fumes that you should not inhale during the curing process. Most UV resins won’t release fumes once cured.

Time to Cure

Depending on the resin type and layer thickness, curing a 3D printed object with a UV flashlight can take anywhere between 30 seconds and a few minutes.

3. UV Lamps

UV lamps use the same principle as UV flashlights but are a better choice for larger objects. These lamps are generally more powerful than flashlights (16 watts or more), but the light uses the same wavelength. 

The only disadvantage compared to the flashlights is that you need to prepare a curing area – which could be an issue if you’re short on space. That said, a lamp is a better choice if you plan to use UV resins on a regular basis.

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UV lamps can use UVA radiation, UVB radiation, or both. The best UV lamp for UV resin should use both UVA and UVB for a faster, uniform curing.

Time to Cure

Similar to UV flashlights, UV lamps take about 30 seconds to a few minutes to cure the resin, depending on the layer thickness and resin type.

Frequently Asked Questions

How long does UV resin need to cure?

The exact curing time varies from resin to resin. Most 3D printing UV resins need about 2-5 minutes to cure under a curing station (UV lamp). Larger objects may require up to 20 minutes, but the time could vary based on the layer thickness.

Curing UV resins with a flashlight requires more or less the same time, but this method is better employed for smaller objects.

If you decide to cure the resin in sunlight, account for a couple of hours at least. Larger objects may take longer to cure in sunlight.

Does blacklight cure UV resin?

Blacklight is a type of UV light (UVA), and it will eventually cure UV resin. However, it often needs more time to cure the resin compared to UVB light, which is used in most UV flashlights and lamps designed for resin curing. You should get a flashlight or lamp that uses both UVA and UVB light for the best results. 

Can you cure UV glue without UV light?

No, you can’t cure UV glue without a UV light. UV glues and resins require UV radiation to harden. Leaving the glue in sunlight can do the trick if you don’t have a flashlight or lamp – which is why some people believe that the glue will eventually harden. However, the UV glue cures because of the light exposure and not because of the temperature or other environmental conditions. To prevent object damage, you should always use a UV lamp or flashlight for a faster and more uniform curing.


UV resin is an excellent choice for printing smoother, more beautiful objects. This material is easier to work with compared to plastic filaments and epoxy resins, but curing requires the use of a UV lamp or flashlight. Although sunlight will eventually cure the material, it could compromise your print’s quality and final aspect.


Two-Part Resins – AddevMaterials 

Safety Tips for Using UV Curing Systems – Berkeley Lab

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