Over 25 years, Pixar's cloth animation has come so far that it was able to build an entire character out of a pair of pants for 2020's "Onward."

We take a look at the labor- and time-intensive process of animating clothes for Pixar characters, and how that process has evolved with each successive film.

Find out how the studio has advanced its digital cloth technology from "Toy Story" to "Coco" to "Onward."

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Following is a transcript of the video.

Narrator: From their first animated short in 1997 to "Onward" in 2020, Pixar has evolved a lot. Animals look more real, we went from smooth fur to seeing every moving strand, and human characters went from stiff...

Andy: Woody! Buzz!

Narrator: To natural and cute. But there's another area of innovation that you might not have noticed in the 25 years Pixar's been around: clothes.

The studio has come a long way since the suit jacket in 1997's "Geri's Game." Such a long way that an entire character in 2020's "Onward" is just made of a pair of pants.

To see just how far they've brought their cloth technology, you just have to look at how they animated the dad in "Onward."

A central character in a Pixar movie will have their clothing built from scratch, starting with a whole set of sketches and concept art. This design stage is especially important when the costume figures prominently into the story, as Dad's does in "Onward."

The film's premise is that these brothers use a magic spell to connect with their late father but are only able to conjure up the bottom half of him, his pants. They improvise an upper half for their dad out of an old sweatshirt, some pillow stuffing, gloves, and a trucker hat, which meant all of this had to seem thrown together, but in a funny, endearing way.

Kris Campbell: He needs to be appealing, right, we need to believe both that he could be a sweatshirt, but maybe, from squinting out of the corner of your eye, you're like, "Oh, that might be a real person."

Narrator: Once the character's wardrobe is designed, all the art reference gets handed over to Pixar's character-tailoring artists, who basically act as digital tailors for the film. It's their job to worry about every single piece of clothing you see in a movie like "Onward."

Their first task is to bring the clothes into virtual form by modeling them in the computer. They build a 3D shape, or model, of each garment, then fit it onto the character model, also known as the skin. As part of the fitting process, they'll take the character through a series of animated poses to see how the clothing fits. This is where things got tricky with Dad.

His lower body was like a traditional character. There was an animated skin underneath those pants. But his upper half was supposed to be made of cloth and stuffing, with no skin or bodily structure underneath it. Here's where the next stage, simulation, came in.

Simulation is a way to automate the movement of elements like clothing, fur, and hair that would take too long to animate by hand. Pixar first used cloth simulation in 1997's "Geri's Game," a five-minute short that was shown before "A Bug's Life" in theaters.

At first, Geri's baggy suit wouldn't fit with his movement outside of a default T-pose; when he lowered his arms, for example, the fabric bunched up in his armpits. Steve Jobs suggested they ask designer Giorgio Armani for tailoring help. Instead they came up with a long-term solution: writing a software for a simulator that would govern the jacket's behavior.

By 2001's "Monsters, Inc.," Pixar had set up a dedicated simulation department and built a simulator engine called FizT, which helped control the folding of Boo's loose T-shirt.

FizT is the same program used on "Onward." It basically functions like a computer, calculating how cloth should realistically respond to a character's movements and surroundings, how it should move with the character's body and in response to different forces.

Campbell: For that, we need motion from the animation department on the character. The character animator moves the lower body around, like, they walk the legs around. And we start simulating it.

Narrator: But because Dad's upper half is all clothes and no body, simulation played an even more important role than usual.

Campbell: We had to make him believable, like, that it's really all the motion is driving from his hips. Since his arms don't have muscles in them, they just need to kind of flop around, which can be a really challenging thing to animate.

There are a bunch of shots in the movie where the entire upper body, the blue vest, the gray sweatshirt, the hands, which are actually just, like, work gloves, and the hat and the glasses, are all simulated.

There's a lot of sort of interplay between the animation and the simulation there in making it feel both kind of intentional, but also believable that it's not really a person in there.

Narrator: Since Dad's upper half is basically a lump of stuffing, it required what's called a volumetric sim, a simulation for something that's thick and has volume.

To make the stuffing look nice and cushy, they used technology from an unlikely source: the octopus Hank from "Finding Dory," a film that Kris actually worked on.

The scene that introduced Hank in that movie took a full two years to make, and in the final version, a lot of Hank's charm comes from his squishy, squashy motion.

Campbell: The volumetric simulation, the squishiness of Hank, was the precursor to the squishiness for Dad.

Narrator: Another beloved Pixar film that Kris worked on, "Coco," also helped to lay the groundwork for the advanced level of cloth simulation in "Onward."

Campbell: The intense layering of cloth and complexity and detail that we got from "Coco" made it possible for us to make more complex and interesting characters on "Onward." And just the speed of our simulator got a lot better. So Dad wouldn't have been possible without the work that was done on "Coco."

Narrator: As viewers, we have an intuitive understanding for how clothes should move on a body, and if simulation does its job, those cloth dynamics will look natural on screen. But when looking at clothes, we also instinctively know how light should reflect off a certain surface and where we might see scratches or fraying threads or pilling. That's where we get to the shading, or surfacing, part of the process, when Pixar's shading artists add highly detailed patterns, tints, and finishes to make each garment look true to life.

We see a variety of different fabrics on the characters in "Onward," and each is treated differently by Pixar's shading artists. They have the advantage of many years of shading technologies developed for earlier productions, like 2012's "Brave."

Back then, the challenge of shading Merida's period dresses and her father's 16 layers of costume produced what the studio calls loom technology. This program basically weaves every strand of virtual fabric into a shading software, giving clothes richer detail and a more tactile quality.

Pixar also made breakthroughs in shading with 2018's "Incredibles 2." Since fashion is such a big part of the "Incredibles" movies, one of Pixar's design goals for the second film was to make their garment shading work better with extreme character movements, like those of the highly kinetic Elastigirl.

Pixar developed technology to preserve fine texture and illumination details in the characters' supersuits, even when the fabrics were stretched or compressed.

In "Onward," shading really helps to sell the textures of the clothes on screen: the shiny leather of Dad's shoes, the fuzziness of his sweatshirt, and the puffiness of his vest. Without any shading work, that vest might look more like plastic than the nylon material it's supposed to be.

Once the shading artists get all the materials down, they add signs of wear and tear, like scuff marks on Dad's shoes and subtle stains on his vest. When watching the movie, you probably wouldn't actively notice these touches.

Campbell: But without them, without those imperfections that are very, very specific, handmade imperfections, it doesn't feel real.

Narrator: Another way to make the clothes look lived in is through wrinkling, which is usually a collaborative project between the tailoring and shading artists. If we take another look at the vest, those bigger wrinkles and bumps were modeled into the garment by Kris as part of the tailoring process.

Campbell: The high-frequency detailed wrinkles were done in shading. So, the part where you could see the puffiness cinched down into the seams? Those very fine wrinkles are shaded wrinkles.

Narrator: Wrinkle patterns are customized for each individual garment, depending on what fabric they're supposed to be and where the artistic direction is going.

Campbell: The wrinkles on the face, we wanted them to be wrinkly enough that they felt like they could be a real sweatshirt, but they couldn't be so wrinkly that it looked like a scary monster. So, for the tailor what that means is we think about how the wrinkles should develop.

So we'd have a bunch of different head shape poses, head tilted to the left, head tilted to the right, and the transition between those poses to make sure that the wrinkles that we were making felt right.

Narrator: Once every single garment has the right amount of texture, it should be looking like real-world fabric, which means the clothing process is pretty much complete. All that's left is rendering all the shots, the final step in Pixar's production pipeline.

The more advanced Pixar's cloth simulation gets, the more power is needed to render each shot. "Monsters, Inc.," for example, required more rendering power than Pixar's three previous features combined, partly because of how complex the cloth and fur simulation was relative to earlier films. Luckily, the studio keeps developing newer and faster processors to do the job.

It's Pixar's blending of state-of-the-art technology grounded in hard math and physics with imaginative fashion and art direction that makes its costume-design language so appealing and lets an outfit like Dad's play its very own role in the storytelling.