How Did Hypercolor Shirts Work?

Readers of a certain age might remember Hypercolor or Hypergrafix clothing, the color-changing T-shirts produced by Generra that were all the rage in the early '90s. Now that the '90s are back, it's a good time to finally figure out the science behind the clothes.

Blinding You With Science

The secret to Hypercolor shirts and products like them is thermochromism, the ability of a substance to change color due to a change in temperature. The shirts are manufactured with two dyes: one regular dye that provides the constant "true" color of the fabric, and a thermochromic dye enclosed in microcapsules bound to the fabric's fibers. The thermochromic dye is usually a mixture of a leuco dye (a dye whose molecules can take on two forms, one colorless; Hypercolor shirts often used crystal violet lactone), a weak acid, and a dissociable salt dissolved in the fatty alcohol 1-dodecanol.

At low temperatures, the dodecanol is solid and the dye exists in its colorless leuco form. At warmer temperatures (>75.2°F), the salt dissociates, the pH is lowered, and the dye's lactone ring opens, allowing the dye to become colored, producing a color change in the warmed area. The new color is dependent on the combination of the color of the fabric and the color of the non-leuco form of the dye—so blue fabric and yellow leuco dye make for a green warm spot.*

More Than Nostalgia

Leuco dyes and other thermochromic applications, of course, have many uses beyond novelty T-shirts. Leuco dyes are used on Duracell batteries along a resistive strip to indicate their heating and gauge the amount of current flowing through it. Thermochromic dyes are also used on food vessels to indicate the temperature of their contents, or monitor their time-temperature storage history. They're also used in building materials, where solar heat turns the material white and results in the reflection of solar radiation and maintenance of the building's temperature. Other thermochromic materials are used in thermal sensors designed for immersed applications, like in fish tanks or washing machines.

* Sometimes, the opposite effect, where the thermochromic dye changes from its colored to non-colored form in response to heat, is desired. In these cases, phenolphthalein, thymolphthalein, or other compounds that are colorless in acidic ranges are often used.

Getty Images
Big Questions
How Are Balloons Chosen for the Macy's Thanksgiving Day Parade?
Getty Images
Getty Images

The balloons for this year's Macy’s Thanksgiving Day Parade range from the classics like Charlie Brown to more modern characters who have debuted in the past few years, including The Elf On The Shelf. New to the parade this year are Olaf from Disney's Frozen and Chase from Paw Patrol. does the retail giant choose which characters will appear in the lineup?

Balloon characters are chosen in different ways. For example, in 2011, Macy’s requested B. Boy after parade organizers saw the Tim Burton retrospective at the Museum of Modern Art. (The company had been adding a series of art balloons to the parade lineup since 2005, which it called the Blue Sky Gallery.) When it comes to commercial balloons, though, it appears to be all about the Benjamins.

First-time balloons cost at least $190,000—this covers admission into the parade and the cost of balloon construction. After the initial year, companies can expect to pay Macy’s about $90,000 to get a character into the parade lineup. If you consider that the balloons are out for only an hour or so, that’s about $1500 a minute.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at

Rey Del Rio/Getty Images
Big Questions
Why Do the Lions and Cowboys Always Play on Thanksgiving?
Rey Del Rio/Getty Images
Rey Del Rio/Getty Images

Because it's tradition! But how did this tradition begin?

Every year since 1934, the Detroit Lions have taken the field for a Thanksgiving game, no matter how bad their record has been. It all goes back to when the Lions were still a fairly young franchise. The team started in 1929 in Portsmouth, Ohio, as the Spartans. Portsmouth, while surely a lovely town, wasn't quite big enough to support a pro team in the young NFL. Detroit radio station owner George A. Richards bought the Spartans and moved the team to Detroit in 1934.

Although Richards's new squad was a solid team, they were playing second fiddle in Detroit to the Hank Greenberg-led Tigers, who had gone 101-53 to win the 1934 American League Pennant. In the early weeks of the 1934 season, the biggest crowd the Lions could draw for a game was a relatively paltry 15,000. Desperate for a marketing trick to get Detroit excited about its fledgling football franchise, Richards hit on the idea of playing a game on Thanksgiving. Since Richards's WJR was one of the bigger radio stations in the country, he had considerable clout with his network and convinced NBC to broadcast a Thanksgiving game on 94 stations nationwide.

The move worked brilliantly. The undefeated Chicago Bears rolled into town as defending NFL champions, and since the Lions had only one loss, the winner of the first Thanksgiving game would take the NFL's Western Division. The Lions not only sold out their 26,000-seat stadium, they also had to turn fans away at the gate. Even though the juggernaut Bears won that game, the tradition took hold, and the Lions have been playing on Thanksgiving ever since.

This year, the Lions host the Minnesota Vikings.


Kevin C. Cox/Getty Images

The Cowboys, too, jumped on the opportunity to play on Thanksgiving as an extra little bump for their popularity. When the chance to take the field on Thanksgiving arose in 1966, it might not have been a huge benefit for the Cowboys. Sure, the Lions had filled their stadium for their Thanksgiving games, but that was no assurance that Texans would warm to holiday football so quickly.

Cowboys general manager Tex Schramm, though, was something of a marketing genius; among his other achievements was the creation of the Dallas Cowboys Cheerleaders.

Schramm saw the Thanksgiving Day game as a great way to get the team some national publicity even as it struggled under young head coach Tom Landry. Schramm signed the Cowboys up for the game even though the NFL was worried that the fans might just not show up—the league guaranteed the team a certain gate revenue in case nobody bought tickets. But the fans showed up in droves, and the team broke its attendance record as 80,259 crammed into the Cotton Bowl. The Cowboys beat the Cleveland Browns 26-14 that day, and a second Thanksgiving pigskin tradition caught hold. Since 1966, the Cowboys have missed having Thanksgiving games only twice.

Dallas will take on the Los Angeles Chargers on Thursday.


Patrick Smith/Getty Images

In 2006, because 6-plus hours of holiday football was not sufficient, the NFL added a third game to the Thanksgiving lineup. This game is not assigned to a specific franchise—this year, the Washington Redskins will welcome the New York Giants.

Re-running this 2008 article a few days before the games is our Thanksgiving tradition.


More from mental floss studios