Key article takeaways:

  • Pretreating is a vital step in DTG printing because it creates the necessary surface for white ink to bond and produce vibrant, accurate colors.

  • Visible “boxing” or staining after pretreatment is often caused more by the shirt’s fabric and manufacturing variables than by the pretreatment itself.

  • Shirt quality and cost do not always correlate with better pretreating results, making it essential to test and choose garments that pair well with your specific DTG process.

If you own a direct-to-garment (DTG) printer, or are looking into purchasing one, it’s widely-known that the pretreating is one of the least favorite processes. It is, however, absolutely necessary in achieving a great-looking print on your garment. As a manufacturer of DTG pretreatments, we wanted to clarify what is going on when you pretreat, why you get the dreaded “box,” and why your “favorite” expensive shirt may not be the best for your DTG pretreating needs.

What is pretreating?

Pretreating is the process that allows for successful digital white ink printing on a garment. It is a necessary step before the shirt is printed where a liquid pretreatment is applied to a garment, typically via a spray application, and then heat set to create a “foundation” upon which the DTG printer (Brother, Epson, Aeoon, M&R) then prints the graphic to be applied to the shirt.

a black shirt getting pretreat applied
Shirts undergoing the pretreat process. Credit: Brian Walker

What Does Pretreating Accomplish?

Pretreating accomplishes two basic functions. You can think of it like primer for drywall. A painter would typically apply a coat of “primer” on the drywall to act as a barrier between the drywall and the final coat of paint. This is done so that the final coat of paint does not soak into the drywall, leaving your finished paint job looking rather spotty and uneven due to different absorption rates of the paint into the drywall.

Pretreatment acts just like that primer to create a barrier between the shirt and the white ink printed on the garment. It allows for a better bonding surface for the ink when printed on the shirt.

The pretreatment also reacts with the white ink, causing it to slightly firm up (not being completely wet or “kicked over”), allowing the CMYK ink being deposited onto the shirt not to mix and muddy on a wet white ink (like trying to paint one color over another when the paint is still wet and they mix together).

The result with pretreating? A great base for the white ink to adhere to and become dry enough for precise retention of the CMYK ink as the final print is completed.

What are Some of the Issues with Pretreating?

Many of the complaints with pretreating stem from determining the amount of pretreatment to apply to the shirt in order to get a great-looking DTG print. This issue is beyond the scope of this article, but a good general starting point is to apply between 18-24g of pretreatment.

Some shirts may require a little less or a little more to achieve the perfect base that will give a great-looking white ink print with the best wash durability possible.

Another issue is scorching or “boxing” of the pretreated area. This is when you can see the pretreated area on the shirt after it has been heat pressed and is dry.

Remember: The pretreatment typically needs to be dried to be activated as the primer for your white ink print. Typically, this is done using a heat press though some shops will run the pretreatment through a conveyor dryer and then press the fibers flat prior to printing. Either process works, with both having their own advantages and drawbacks (this topic also is beyond the scope of this article).

How Much Does the Quality of the Shirt Affect the Above Issues?

As a manufacturer, we hear on a regular basis that the pretreatments stain or leave extremely visible boxes on certain garments or certain colors. We will address this with a simple illustration and explanation.

Pretreatment is typically not the issue with staining. It is true that in some cases the pretreatment can be less than optimal for DTG and will definitely contribute these issues, but most of the established brands of pretreatment all perform relatively the same in regards to the staining issue. Some pretreatments perform better on certain colors or brands of shirts than others.

In our experience, where one brand performs better on color “A,” the other brand may outperform the first pretreatment on color “B.” There is no magical pretreatment that solves all the issues associated with DTG pretreatment and printing.

The biggest contributor to visible stains and scorches is actually the shirt itself.

One would think that a higher-priced or perceived higher-quality shirt would perform much better than a less expensive garment. This perception is really a misconception.

Take a look at the picture below; there are three separate T-shirts from three different manufacturers. The application amount of pretreatment, process for curing the pretreatment, and the cure time were all the same across each shirt. The amount of pretreatment applied was 20g; and heat-set with 80 psi on a pneumatic heat press at 320 F, pressed two times for 20 seconds each, with the press covered with a parchment paper during curing.

3 shirt samples with Image Armor logo overlaid
Three separate T-shirts from three different manufacturers demonstrating pretreatment differences. Credit: Brian Walker

The application and process of applying and curing the pretreatment was exactly the same; however, the results on the three different shirts were completely different (and unexpected). Please note that the camera will make the pretreatment area more visible that what is typically seen with the naked eye but in real life, the above differences were rather dramatic to the naked eye.

The shirts are numbered from 1 to 3. As can be seen, one of the worst results on a black shirt was shirt no. 2. The pretreatment area was much visibly lighter that the original color of the shirt, creating an extremely contrasting DTG pretreatment box. Shirt no. 3 was better but still very visible, while shirt no. 1 had only a slightly perceivable pretreatment area if you knew what you were looking for specifically (i.e., being very picky).

Let’s break this down into a chart:

Doesn’t a higher-priced shirt mean a higher quality DTG print?

This is a question that is often asked. The cost of the shirt does not necessarily reflect the quality of performance for pretreating. A higher-price garment does not always indicate the garment will perform or hold the DTG pretreatment better that a lower-priced garment.

So, What is Actually Going On?

During the manufacturing of the shirts, there are a lot of different processes that play into how a garment will react when pretreatment is applied to the shirt. Everything from the dyes, to the water used, to the post processing of the garments all play into how pretreatment reacts on the shirt.

As can be seen in the image in the previous section, the least expensive shirt performed exponentially better than the other two more expensive shirts that are considered “higher quality” in the industry. We will not disclose which shirts each are because that is not the goal of this article.

The entire manufacturing process is responsible for a well-performing shirt in the DTG printing market. We are not saying that these shirts above are poor performing shirts — they will perform well for screen printing or direct-to-film (DTF) just fine.

The Pretreatment Takeaway

Pretreating is an essential part of the DTG printing method. However, just as important as the pretreatment and pretreating process is itself, there are many other factors to consider. The shirt plays an equal, if not more important part in the DTG process.

Finding the best shirt that works with your DTG pretreatments, whether it is Image Armor or another brand of pretreatment, is key in successfully creating a truly one-of-a-kind DTG-printed masterpiece.

If you want to completely avoid any pretreatment box and not have to pretreat, there is the option of utilizing a fully DTG pretreated shirt. One such product is RTP Apparel (shop.rtpapparel.com) where the entire shirt is pretreated, allowing you to skip the pretreating process itself (there are other brands available out there as well). This can save time and money in production even though the shirt typically costs more than a standard untreated shirt.

Don’t be afraid to recommend the best DTG performing shirt to your customers, and keep in mind one brand may not fit all of your DTG printing requirements. You might utilize one brand for black shirts and another for red or navy. Remember you are the apparel decorating professional and your experience holds a lot of weight — especially when you can explain to the end customer why you want to use a particular shirt.

Continue to refine your knowledge, experience, and techniques, and you can take your DTG printing to exciting new levels of quality!