Valtteri Bottas complained that Mercedes' decision to wear black overalls as a political statement affected him as a driver at the Spanish Grand Prix.
Bottas also expressed his dislike for a new rule requiring drivers to wear thicker innerwear.
Mercedes switched from white overalls to a black to match the 'end racism' livery of their cars.
With track heat measured at 50 degrees Celsius, the Finn told his team in a radio message laced with an obscenity that "the black overalls are...hot".
As Bottas struggled, his team-mate Lewis Hamilton remained largely in control en route to victory.
After a poor start, the Finnish driver, still chasing his first world title, made a strong comeback but was unable to catch Hamilton or second-placed Max Verstappen of Red Bull.
Bottas finished third, but said the effort he put in combined with the heat and the black overalls had drained him.
"Obviously, we have changed the colour of the overalls and it's known that black takes more of the heat, especially when there's direct sun," he said.
"I don't know any numbers or facts, or how much it is actually black versus white, in terms of temperature difference, but this year it's been really hot in the car," Bottas said.
"Also there's new homologation this year for the overalls so they are thicker and the underwear is thicker. I don't know how much affect that has, but it was just so hot.
"I lost three kilos in the race, which is quite a lot," he said. "So that already can start to affect performance. I know that, from the all the drivers, I'm one of the fittest, so I can take it, but it's never comfortable and there's always things that we can improve.
"It was really hot in the car and I felt that since this year it's been even hotter," he said.
Hamilton won by 24 seconds ahead of Verstappen and afterwards said he had felt as if in a trance as he drove to victory.
"It's not an out of body experience," he said. "I just think I was in my highest form, I would say."
