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Behind The Tees: What Is An Underbase? And Why Is It Important?

7/10/2019 by Imri Merritt aka M

The majority of T-shirts people order for printing are black, dark, or color. And of course, they also want bright colors in their print that pop off the shirt. The problem is that most Plastisol inks are semi-transparent, and so simply laying down one hit of ink just doesn’t cut it. On black tees, the ink color can look dull and washed out. And on colored shirts, the ink can actually take on a different hue. New ink, hue dis?

So how does this problem get solved? Enter the underbase.

What is underbase in screen printing?

Simply put, an underbase (or underlay) is a layer of high-opacity ink (usually white) that is printed on the garment and flash-cured before the other colors are printed. It’s a similar concept to painting a base coat of primer under your main paint color. But this is ink– don’t call it paint unless you want screen printers smirking and rolling their eyes.

Why underbase?

There are several reasons to use this technique. The first, as I mentioned is color vibrancy. Printing and flash-curing a white underbase will ensure the overall vibrancy of the print. The second is color accuracy: printing on top of a white base will mostly eliminate the possibility of the shirt color affecting the top colors. The third reason is to reduce fibrillation: creating a nice smooth surface for the ink to sit on top of, rather than having those little fuzzy shirt fibers poking through and giving the print a grainy look.

Underbase vs no underbase: How to know when to use it

Seems great, right? So would you ever not want to underbase? Underbasing is a relatively newer technique in the entire history of printing but has been so widely adopted in the past few decades that it’s become a standard. Back in the day, printers would just use high-opacity inks, or hit each color twice and hope for the best. Most T-shirts were white or light-colored so they could get away with it. But on darker garments, the colors were muted. This is what is known as the ever-popular “vintage” look, also referred to as “soft hand”.


Who knew the future would be vintage?


So if you’re going for a vintage look, you may want to request the underbase be left out. Just keep in mind the trade-off: a softer, more lightweight print in exchange for less vibrancy and reduced color accuracy. There are other ways to create a vintage look while keeping an underbase, such as adding a distressed effect to the artwork, using thinned-down inks or using a discharge underbase with water-based inks.

Does an underbase cost extra?

While I can’t speak for other print shops, here at RushOrderTees your underbase is free. (Keep in mind that if you have white ink visible in your design you will be charged for that color, as two whites will need to be used: one for the underbase, and one for the highlight white, also known as finish white.) Most other places I know of do not charge extra for the underbase, so if you find that your printer has charged you for it… maybe it’s time for a new printer.




Here’s some information that may only apply to screen printers or graphic designers, but if you’re the curious type and interested in learning more, read on. Or you’re the TL;DR type, you can scroll through this part to the examples and the explainer video at the end– because here’s where things get a little tricky. And one thing that’s tricky is registration.


This refers to the degree to which the screens line up with each other (and therefore the colors of the print). If one or more of them is a tiny tiny bit off, maybe nobody will notice. If it’s more than a bit off, you start to get a blurry look and even a double-vision look if it’s a lot off. (Make sure you’re not drunk when you check registration– it could just be you.) Of course, getting registration right is the first part. Because even if it’s dead-on, there’s another pitfall to be aware of.

Ink gain

This is when the ink spreads out slightly as it comes in contact with the garment. There are things a printer can do to minimize this, but realistically there’s always going to be some ink gain. And when the edges of colors push up against each other it’s not that big a deal because one will be covering the other. But if that white underbase peeks out behind the colors, then it’s a problem. It can create a halo effect around the edges of the print, and nobody wants that. So, what to do?

Underbase choke and/or trapping

Some call it choking, some call it trapping, I like to make a distinction between the two. But first, let me define the general concept: essentially it means modifying the design slightly (in the separation) to make sure the underbase is not peeking out along the edges.

There are two methods for doing this and both are useful in different circumstances: choking is retracting the underbase, trapping is expanding the top color– both of which achieve the same goal. So when to use one method rather than the other? Glad you asked. It all comes down to the details. Let me illustrate it using an example.

This first image shows you what a difference underbasing makes. This is a simulation of a left chest print of our logo, approximately 3 inches wide, that I’ll be using to show you a few different looks. The red here is Pantone Red 186 c printed on a heather black fabric. On the left, you can see how dark the ink looks with one hit and no underbase. On the right, we have the bright, accurate color of red because it is underbased.


All good, right? Not so fast. Remember we talked about registration and ink gain? The graphic above doesn’t account for those things: the white base and the red are perfectly registered, sitting on top of each other, which doesn’t happen in real life. It’s always going to be off just slightly (hey, nobody is perfect). And that white ink could “gain” easily because it needs to go down heavier. So here’s what that could easily look like:


As you can see, the white underbase is peeking out of the edges, and something no printer (or customer) wants to see. This is the reason the underbase needs to be choked. Or, trapped by the top color. So which one should we go with? Most print shops will have their art department choke the underbase by default, which is typically the way to go– with some exceptions. Let’s look at the same print but with the underbase choked by 2 pixels. Do you see any problems?


If you noticed the problem is that the small type and banner got weird looking, you are correct. Let’s take a closer look:


The larger areas don’t have the same problem, it’s all about the detailed areas. Essentially the lines are so thin that they cannot afford to get contracted 2 pixels without creating gaps, which can be noticeable in the print. If it is, a lot of time the printer can fix this by flooding the red, which can get sloppy, or by hitting the red twice (print > flash cure > print). But printing red twice not only defeats the purpose of the underbase, but it also adds lots of extra work time to the job.

The better route is to set it up properly in the art department before it gets to press. This is where trapping comes in. So in the next image, we’re going to see how it would look if we leave the top part the way it is (underbase choked), but for the bottom detailed area, we’re going to expand the top color by 2 pixels (underbase trapped):


Again, this is a “pro tip” so if you’re a customer, none of this needs to concern you. Our art department handles all of this when we do the separation and set up the job for printing. All you do is kick back and wait for your tees to arrive.

No rush, but how about today?

Omitting parts of the underbase

We’ve learned that you get a darker shade of color without an underbase. So why not use it to our advantage? Here’s a trick I do all the time, and it works fantastically. The one requirement for this to work is that the garment must be black or dark gray.

Below are two print preview images of an actual 9-color job. The lizard dude on the left is a normal set up with a full white base under everything. The one on the right is a print preview file of a 9-color separation using the method of omitting the underbase. The darker shades are slightly transparent, showing the fabric’s texture. His glasses have a nice contrast.

This omit-the-underbase technique is perfect for this print, because the shadow areas are not super important, and would look fine either way. You don’t want to leave out the underbase for important areas such as type, or large areas, or areas that must be visible, clear or prominent. Other variables at work here can affect the results, such as ink opacity, screen mesh counts, squeegee angle, pressure, and other press conditions can play a role, but we take care of all that stuff for you, so you can concentrate on surfing with your lizard buddy. Here’s a GIF showing the colors going down in their print order.


Halftone underbasing

What if we need various shades or gradients? That’s where halftones come in. Halftones are basically just dots of different sizes that fool the eye into seeing variations in tones. You can read more about halftones in Round 4 of  screen printing vs digital printing.

Here is an example of a small, simple print with halftones in the underbase that are used very effectively. On the left, you can see that the bottom of the bars fade out towards the bottom. In the middle image, you can see that the top colors are all solid. On the right is the combined result, with the underbase halftones doing the work to give each color its own gradient.


Preview of the print order.

Simulated process screen printing

Now we get to the crazy stuff. The next example is another actual job we printed here and for the separation, I used a technique called simulated process. Essentially, its using layers of ink, each with halftones, to create a rich, multi-color photographic style print with all the tones and shades and gradients your heart desires. And the really cool thing about it is you print with fewer colors than it appears to be because all the layering and blending going on. That’s the magic of halftones. This print is only 4 colors!

Take a close look at the underbase image on the left. If you notice there are areas of various tones, and also areas where the underbase is missing entirely. In the middle, you can see how the ink colors are covering a lot more of the areas. And on the right, it shows how the underbase and top colors are working together to create a wide array of tones.


That’s it for now. Please enjoy this video we just released, featuring my boy James Metzer explaining underbases for the TL;DR crowd. The video was shot, directed, and edited by Dan Leer, who we found wandering the streets looking for a job. This is the first of an explainer series, so keep your eye out for the rest of them. I might even show up in a few.


Happy designing,




About the Author

Imri Merritt aka M Imri (pronounced em-rye), also known as “M”, joined RushOrderTees in the spring of 2015, bringing over 10 years of graphic design and color separations experience in the screen printing industry. Over the next three years, he helped transform the Art Department, improving the overall quality, efficiency, and customer service of the team, while making some beautiful T-shirts along the way. A graduate of the Multimedia program at University of the Arts in Philadelphia, he has explored various creative pursuits, including art and design, marketing, DJing, and even producing comedy shows. He brings his well-rounded skill set and forward-thinking approach to every project he's involved with at Printfly / Rush Order Tees. He is a contributing writer for Impressions Magazine, Printwear Magazine, and ASI Central. He loves roller coasters, music, and fried pickles.