The National Hockey League (NHL) brings together the best hockey players in the world, and the NHL relies on cutting-edge technologies to help protect the players and ensure that the sport is played at the highest levels. That is certainly the case with players’ equipment, the care of the rink, and other aspects of the game.

What hockey fans probably don’t know is that the NHL uses color-changing thermochromic coatings on the pucks. Before the game, the pucks, which are made of vulcanized rubber, are frozen to help them glide easily along the ice. As the pucks gain heat, they slow down and can bounce. These coatings inform referees when the pucks should be taken out of the game.

In December 2022, PPG and the NHL announced a three-year extension of their North American partnership. Brittney Miller, marketing communications manager for corporate and government affairs for PPG, noted that PPG been the “Official Paint of the NHL” since February 2017, and that PPG partners with Hallcrest, a SpotSee company, on the thermochromic coatings.

“When a puck starts warming to over 22˚F, it will start to bounce, making it difficult for players to accurately control, pass and shoot during the game,” Miller said. “PPG worked with our partner, LCR Hallcrest, to come up with a solution to this problem — an ink that tells referees when the puck is too warm and should be replaced. The ink is purple when frozen and turns to white when it is too warm. Once pucks are removed from play, they are never used again. Over 60,000 pucks are used per NHL season and have included the thermochromic coatings for the past four seasons.”

Hallcrest is highly regarded for its thermochromic technologies, which have been used for battery testers, food safety and many other applications. The NHL first started using Hallcrest’s technology on its pucks in 2018. In January 2021, SpotSee acquired Hallcrest, a move that Billy Sanez, director of global marketing for SpotSee, noted brought new technologies to SpotSee, including thermochromics.

“It was an opportunity to incorporate an amazing set of temperature monitoring and thermochromic technology to our portfolio,” Sanez noted. “With the Hallcrest incorporation, we brought in the development and manufacturing of color changing temperature products, thermal labels and thermometer strips, from color changing inks, to forehead thermometers, freeze indicators for food and pharmaceuticals, as well as fantastic applications like the ones used by the NHL, to the color changing labels of Coors Light bottles and recently a great application for Hellman’s Mayo in Europe.

Sanez pointed out that one of the biggest challenges is the reliability and accuracy of the indicator, or the change of color.

“Our solution – the ink that changes from purple to white – shows the players and officials when the puck gets to 28°F clearly and accurately, and lets the officials know when to change the puck,” Sanez said.

Ultimately, thermochromics can be found nmuch of our daily lives, even in the medicines that we take.

“Thermochromic technologies help us create anything from a color changing puck – so players know when the puck gets too hot and may bounce around the ice – to indicators that let patients know that their medicine that should not get too hot or freeze experienced temperature incursions,” Sanez concluded. “The technology is also used in blood bags (our HemoTemp II product) that monitors the temperature at blood banks and hospitals.”