It may have been priceless to Jackie Robinson, but a New York auctioneer hopes to get $400,000 for a Brooklyn Dodgers cap that was specially padded to protect the man who broke baseball’s color barrier from beanball-throwing racist pitchers.

The royal blue “B” cap looks like any other Bums lid of the time, but for the inner lining that’s fortified with a fiberglass-and-cloth composite that gave Robinson some extra protection from pitches aimed at his skull.

“It was a special hat for him. It has a helmet liner to protect him from beanings from racist players who would throw the ball at his head,” said Lelands chairman Josh Evans. “This is ancient, early baseball technology.”

The hat is on display at the National Sports Collectors Convention in Atlantic City this weekend, with hopes to sell it by Sunday. The price tag is a firm but not deal-breaking figure, sellers said.

The cap belongs to a private collector who purchased it in the 1990s from widow Rachel Robinson, Evans said.

Robinson broke baseball’s color barrier in 1947 when the Dodgers brought him up to Brooklyn. He spent 10 years in the big leagues, with Ebbets Field as his home park. In his first eight seasons, Robinson was in the top four every year among National League batters hit by pitches.

“I think it’s a reasonable supposition” that Robinson was drilled so much because of his race, baseball historian John Thorn wryly said. “Robinson was obviously a man of courage.”

Thorn pointed out that Robinson could at least see a pitcher’s beanball coming at him — but not anything hurled from the stands behind him.

The National League required batters to wear helmets starting in 1956, and the American League followed suit in 1958 — although veteran players used to wearing caps were given a choice.