Ever consider what keeps Iron Man from overheating inside his suit? Or protects Cap’s abs when he’s punched in the chest plate? We got an exclusive look at the specialized athletic undergarmets the actors wear — which sounds pervy, until you hear about all the tech that went into making these things.

Marvel and athletic wear company Under Armour teamed up to develop unique base layers for each of the major characters in Avengers: Age of Ultron. Alexandra Byrne, the movie’s Academy Award-winning costume designer, wanted cutting-edge gear that would keep the stars warmed-up, moisture-wicked and ready to fight hordes of evil robots bent on destroying humanity.

Today, Under Armour will start selling replicas of these tactical undershirts used in Ultron, which means your morning run just got a whole lot more badass.

The video below shows the costume-making and garment process. Director Joss Whedon explains that for superhero movies, costumes are “make or break,” and you can see Aaron Taylor Johnson (Quicksilver) showing off his Under Armour and Thor (Chris Hemsworth) talking about his costume. (Fun fact: Black Widow’s updated light-up catsuit required a team of electricians.)

The superhero gear collaboration started with Captain America: The Winter Soldier, after it became obvious that better protection was needed.

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The Avengers actors are known for doing a lot of their own combat scenes and stunts (alongside an insanely kickass stunt team). In the first film, the focus on authentic costuming meant they weren’t always comfortable. The actors are extremely active throughout filming, and subject to the same sweat and muscle-straining issues mere mortals face when working out — plus, they’re wearing complex, heavy costumes that can chafe or overheat.

Neal Goldman, Under Armour’s product designer on the project, describes these undergarments as “something out of the future,” like they came from Stark Industries. The Ultron project sparked a brand-new way of constructing protective layers with a special tubular knit pattern, a highly-engineered knit designed on a specialized machine. Here’s a close-up of Quicksilver’s undershirt, which shows the pattern:

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Under Armour’s creations are designed specifically for people trying to stay dry and combat sweat. The shirts have to be a close fit, even if they aren’t for people wearing giant robot costumes. This is part of what athletes call “compression technology,” which works when tight garments keep muscles warm, fighting the strain that would otherwise result from intense activity. Whether its a leg wrap or a full body suit, it needs to fit like a glove in order to prevent chafing and rashes that other materials can produce.

And here’s Cap:

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Goldman said the aesthetics came straight from Byrne and the Marvel team, which had “high-level renderings” of how their heroes had to look. Under Armour’s innovation and technical design teams then developed the unique knitted process in their clothing labs. They worked with synthetic molds of the actors’ physiques and body doubles to ensure a perfect fit. (Though I asked nicely, there are no pictures and/or copies for sale of synthetic Chris Evans.)

Goldman told me this is by far the coolest project he’s gotten to work on—the Under Armour team even got to fly out to Ultron’s London set. While he’s giddy over the idea of his favorite childhood Avenger, Iron Man, wearing what he helped make, he’s most excited to see Quicksilver (above) on the silver screen.

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That’s because Quicksilver has the only long-sleeved garment of the lot, complete with thumbholds, to fit seamlessly under his skintight costume. Quicksilver’s design had to be totally streamlined for a maximum aerodynamic efficiency, given that his power is superspeed.

The replica gear you can buy will be the Iron Man, Captain America, Quicksilver and Black Widow models. Though you can’t buy it, there was also a special Hulk garment — all of the main characters got personalized Under Armour. Here’s what Bruce Banner/the Hulk received:

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The characters’ abilities factored into their gear designs. Cap’s shirt has a protective panel over the abs to lessen the shock of the hits he takes, while Black Widow’s sleeveless garment allows the ballet-trained and master acrobat Natasha Romanov unrestricted movement. Here’s a closer look at Black Widow:

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The actors put the tech to the test through long and grueling shoots. In the past, the Avengers costumes were sometimes a struggle to wear for long periods of time, and there was a need for next-to-skin performance apparel for the second go-round. Now the actors are far more comfortable, and are able to stay cooler under all their armor.

It’s a good reminder that acting isn’t just about emotional expression — it’s also about athletics. And costumes have to evolve just like athletic gear to make it all happen.

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You can check out the newly available superhero-inspired gear here.

A closer look at additional designs used in Age of Ultron is below, including Thor and Hawkeye’s gear — these won’t be seen anywhere else except underneath our heroes’ clothes on film.

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Iron Man variant:

Captain America variant:

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Thor:

Hawkeye:

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