Toothpaste is closer to liquid than solid, so it’s surprising that it doesn’t mix in its container, and not just doesn’t mix but can actually come out with clear stripes. How do toothpaste manufacturers pull this trick off?
Scientists design striped toothpaste with colorful portions that maintain their own thickness and viscosity, meaning they won’t mix even easily in the tube. The nozzle is then divided so that when you squeeze the tube, the toothpaste comes out evenly and consistently, resulting in tidy stripes.
Let’s get into the details of how toothpaste manufacturers achieve this amazing feat.
Does All Toothpaste Have Stripes?
Interestingly, not all toothpaste brands have stripes. Even in the ones that do, not all the toothpaste in the tube is arranged in those thin, uniform bands. Indeed, the illusion of Aquafresh (on Amazon) and other manufacturer’s signature stripes, for example, only happens as you squeeze out the toothpaste onto your brush.
People have theorized that most of the tube is filled with plain white toothpaste. They argue that the trick lies at the top sloping part of the tube, which has colored gel.
They claim that the toothpaste only gets its stripes by rubbing against the gel, which is squeezed into slots running inside the nozzle at the top of the tube. While this all might seem convincing, nothing could be further from the truth.
Science is usually at play whenever you stumble upon something that looks unexplainably magical, like the engineering miracle behind striped toothpaste. The toothpaste inside your tube has layers with different colors and physical properties. A machine fills the tube from the bottom with all three colored layers, just like those that fill ice cream cones.
Why Does Toothpaste Come Out in Stripes?
Toothpaste manufacturers design their bright stripes in a way that maintains their thickness and flow under different pressures, allowing the squiggles that end up on your brush to come out looking sharp every time.
This isn’t meant to take a shot at your sanity. A great deal of scientific research goes into making oral care products so that they’re functional, highly effective, and visually appealing.
The trick behind the crisp nature of the stripes lies in what scientists call “rheological behavior.” Rheology is the science of how solids and liquids deform under stress. Essentially, striped toothpastes are purposefully made to hold their position and consistency regardless of the pressure you apply to the tube.
The toothpaste indeed has different colors, and by squeezing it out of a divided nozzle, the stripes come out precisely and consistently. The colored paste on the edges of the tube pushes faster and comes out first, so the stripes dispense evenly.
The stripes are ordinarily thick when the toothpaste is at rest inside the tube. However, the toothpaste yields as you squeeze the tube, making it thinner so it can flow out easily. But because the dyed parts maintain their rheology, they’ll ooze with the same speed and consistency, maintaining their position in the dispensed toothpaste.
How Do The Stripes Get Separated?
It mostly boils down to the thickness and viscosity of the paste. These physical properties are also the key to why a huge lump of toothpaste doesn’t run off the end of your toothbrush as you squeeze it out.
As Colgate scientist Sergio Leite explains, toothpaste isn’t as easy to mix as one may imagine, no matter how much you mangle the tube. “It may look like you’re mixing, but you’re not really mixing,” he says.
There’s no hidden technology in the sloping part of the tube or any fancy subdivisions for packing striped toothpaste.
When Leite’s team is developing a new product, it has to ensure the toothpaste in each stripe maintains its physical properties, ensuring no colored layer will squeeze out faster than the other. It’s also the reason the stripes stay intact once you’ve squeezed the toothpaste out.
The toothpaste also employs a clever technology called “thixotropic rheology.” Once you’ve stopped applying pressure, like when the toothpaste sits on your brush, the stripes maintain their thickness, making the toothpaste look like a three-striped cylinder.
But when you brush, the agitation makes it thin out in your mouth for easy rinsing and disposal.
