Olivia Wilde arrives on the red carpet for the 88th Oscars on February 28, 2016 in Hollywood, California. Picture: Valerie Macon/AFP.

Most actresses wore deep, plunging necklines this year, but there wasn’t a stray bra strap or perky nipple in sight — unlike poor Gigi Hadid who had a nip slip while walking in the Versace show at Milan Fashion Week.

Actress Margot Robbie at the 88th Annual Academy Awards. Picture: Ethan Miller/Getty Images.Source:AFP

Saoirse Ronan arrives at the Oscars. Picture: Dan Steinberg/Invision/AP.Source:AP

Charlize Theron arrives at the Oscars. Picture: Jordan Strauss/Invision/AP.Source:AP

So how do they keep those things up?

Do they make like Kim Kardashian, who revealed her strange — and no doubt painful — breast-hoisting technique on her app earlier this month?

This photo is real. Kim says she uses gaffer tape used to tape stage wires to keep her breasts up.

Probably not, according to fashion commentator Josh Flinn, who works for Australian designer Steven Khalil.

He’s previously worked alongside Alex Perry and, during his time as a celebrity stylist, Flinn says he “jammed boobs into dresses for years”.

According to Flinn, most of the ladies on the red carpet are being held up with Hollywood tape, or a bra cup that is sewn into their dress.

“Hollywood tape is double-sided see-through tape that sticks to both the fabric and the skin,” he said.

“You don’t want the tape to pucker, so you do tiny little pieces around 1cm along the bust line. You don’t have to use a big strip of tape. That’s a rookie mistake.”

Oscar winner Brie Larson. Picture: Kevork Djansezian/Getty Images/AFP.Source:AFP

Plunging neckline and thin straps don’t allow for a bra, so the tape holds the breast in place without a wire or cup.

“Also these are not average women,” Flinn said. “They spend hundreds of thousands of dollars to get these bodies and their assets aren’t always their own, so they stay up by themselves a little easier.”

Flinn helped Khalil design an outfit for actress Emily Ratajkowski to wear to the Vanity Fair after-party. It’s a black bodysuit with bra cups sewn into the suit.

“There’s no underwire, just the cups, so she has support and the look is seamless,” he said.

Actress Jennifer Lawrence attends the 88th Annual Academy Awards. Picture: Jason Merritt/Getty Images.Source:Getty Images

Actress Jennifer Lawrence. Picture: Jason Merritt/Getty Images.Source:Getty Images

Judy Len, who styles Ariana Grande, Jamie Chung, and Nicole Scherzinger, told Refinery 29 that taping is the common trick of the trade.

But “with red carpet appearances, I worry that if the girl sweats, it won’t stay on as long,” she said.

Penny Lovell, who dresses Rose Byrne, Anne Hathaway, and Kristen Wiig, says double-sided tape is her No. 1 must have item in her styling kit.

“I always carry double-sided tape in my wallet — you may never know when you need it,” she told InStyle.

Actress Cate Blanchett arrives on the red carpet for the 88th Oscars on February 28, 2016 in Hollywood, California. Picture: Valerie Macon/AFP.Source:AFP

“One year before a red carpet event, I dropped by to say hi to a client — I wasn’t working, so I didn’t have my kit with me — and the tailoring wasn’t done correctly and the dress’s neckline was too revealing. But thanks to the tape in my wallet, it was fixed. Thank god I had it.”

And of course, there’s always the old faithful Spanx.

“I’ve seen quite a few people squeeze themselves into almost bull body stocking Spanx,” said Flinn.

“They come just under your bust and finish under your knees. They can work, but the fat has to go somewhere. You get that really weird ankle with really big bits of flesh at the top.

“Sometimes I feel like saying ‘Ladies, don’t even bother’.”