It starts with a bit of a mystery: How does cooling shirts work in NASCAR?

Some drivers don't know. Others think it has to be Hendrick Motorsports — or more specifically, Jimmie Johnson, who always seems to be at the forefront of fitness and nutrition.

"I was the first driver to wear it, but the guy who started was Chad North."

According to Johnson, his captain always focused on new technology and a holistic approach to performance, including Johnson. The seven-time Cup series champion also dealt with cramps and was susceptible to heat problems, so Knaus got a cooling shirt and decided to test its effectiveness.

"When we used to paint cars, one of the bays was rolling cars in, and they would be there to make it there hurry up and solidify the paint," Johnson said. "(Knaus) Literally, one of our guys put on this damn shirt, inserted it into the wall, sat there, pretending he was testing in a racing car. I would never forget Chad called me, 'You won't believe, this cool shirt thing is OK! I'm doing something on a spray baking sheet, I'm there, I cooked him there, I cooked my feeling!

Johnson started wearing shirts around 2018 or 2019. At first, only his teammates knew about it. He doesn't want his competitors to know, because it's an advantage on the steering wheel. Over time, it became public knowledge and saw the driver's monkey under Johnson's leadership.

Joey Logano breaks into his signature smile and laughter.

"It's like jumping into the pool on a hot summer day," said the NASCAR Cup Series champion of the reigning period. "It feels great. It's great."

The easiest way to describe it is a shirt with cooling technology. This shirt holds the tube through which the coolant passes. It completely changes the driver's comfort.

"I think a few years ago, when we were wearing suit ice packs and throwing it between two stops," Erik Jones said. "The endurance side, on a hot day, it's just a game-changer. Sometimes you get rid of those hot games, finish and eliminate, even train or no training or no training.

The process of driver comfort has evolved over the years. Ice bags, fans and helmet hoses are still used to blow cool air on the driver's head, which is some of the ways the driver tries to keep the temperature dropping. However, considering the helmet hose on the latter surface does not have the same effect as the cooling shirt. Today, it is difficult to find an unweared driver on the field.

Jones is not alone in using “game-changing” when talking about cooling shirts. Such driver Michael McDowell uses a shirt to associate the driver's rise with an introduction to the next generation of cars in 2022. The Cup Series soon realized that the car was more heated, making the shirt more attractive.

"(Shirts) are nearby, but they will fail often, otherwise it won't be that cold," McDowell said. "You'll worry about running them because you don't know if it's a good day or a bad day, but now, I know there's some trouble every now and then, but Phew, it's incredible, which helps keep your core cool, vital organs cool, and just slows down your heart, which reduces some calories in your heart."

Shane van Gisbergen even freezes his shirt beforehand to make it even colder. It’s so important that his PR rep reminds you to “keep a cool shirt in the refrigerator for an hour and a half before a driver’s meeting” in her personal calendar.

Some drivers don’t wear shirts every weekend and make decisions based on the weather. Ross Chastain is one, saying that sometimes he wants to sweat.

"Martinsville, I had to use the bathroom because I wasn't sweating enough," he said.

When on the car, the shirt (or vest, depending on the choice) is connected to the pump under the fire esuit. Hendrick Motorsports’ in-house expert Cesar Villanueva explained that the pump can be installed anywhere.

The pump passes through a mixture of water and an antibacterial and antifungal fluid. It helps keep the system clean and it can get clogged if the fluid is not circulating. Naturally, if it is blocked, the pump will not run. However, there is more than one reason that the system may fail the driver during the race.

"You're just stuck in a bad situation," Austin Dillon said of the system failure. "There's nothing you can do about it, you can just turn it off, and you can pour water out if you need it, but it's like a lifeline. It's very important to have it."

The failure means the driver is starting to boil. The liquid gets hot and if the water cannot be poured, it won't escape.

"Until not," Logano said. "But more times. Honestly, they did a great job of doing it, developing the whole system. It used to be heavy, which is why no one used it, and now you have a very effective process, if it can help you mentally at the end of the game because you're physically angry, then you'll do it.

"I don't care how good I'm in shape, and I'll get tired after 400 or 500 miles. If you can keep some fresher, it might be worth it."

Of course, weight is important. Of course, driver comfort is crucial, but so is the performance of the car, with the weight taking precious lap time. Due to its impact, it is necessary to accept the use of the unit, and Villanueva said it may be about 6½ to 7 pounds.

"I think we've accepted some weight penalty because you have to make sure you're as fresh as possible at the end of these games," Chris Buescher said.

After Tyler Reddick lost weight, he started using one in 2021. He noticed that he suddenly needed something to keep the core temperature adjusted better because, as he said, its heat quickly became very hot.

However, Reddick's compliments are the ideal way to sum up NASCAR cooled shirts.

“A lot of drivers use it,” he said. “I think the effect of cooling the body is probably the most effective thing we have.”