New York — “Mad Men” has gone beyond a fashion fad. The AMC show about a 1960s ad agency — in which style is as important as the characters and plot — continues to influence runways and retailers with a branded collection debuting this month at Banana Republic.

Movies and TV are not uncommon inspiration for fashion designers — especially when it’s a highly stylized look. But the influence of “Mad Men” has had a straight run for more than four years, reintroducing the masses to skinny ties, pocket squares and body-hugging dresses.

The new clothing line also provides a temporary fix for “Mad Men” devotees awaiting the show’s return in 2012. No new episodes of the show aired this year.

The clothes are sexy, and Joanna Coles, editor-in-chief of Marie Claire, says that’s one of the things that really has resonated with both viewers and shoppers. The show gives us permission to dress to impress the opposite sex — and in fact encourages it, she observes.

“‘Mad Men’ shows you how to look great in the workplace, and it shows you how to work it,” Coles says.

It’s the rare TV show that glamorizes the office and fills it with attractive people, she says: “When you look at something like ‘The Office,’ no male executive wants to recreate the style of Steve Carell. No one wears lipstick at Dunder Mifflin. ‘Mad Men’ makes the office a more exciting place than it often is, and Banana Republic is trying to channel that.”

Madison Avenue during that era was practically a catwalk with men in three-piece suits and fedoras, and women in sheaths and high-heel pumps carrying handle-top handbags.

It’s a good look — and one that people look good in, says Simon Kneen, creative director for Banana Republic. “It’s about good tailoring, it’s bon ton, and a little more buttoned up and polished.”

But, he says, a key part of the collaboration between Banana Republic and the show’s costume designer Janie Bryant was to be sure they weren’t crafting costumes. The clothes are modern, with shapes and details adapted to a contemporary eye, Kneen explains.

Gone is the enhanced hourglass created with bust darts and high waistline, according to Bryant, and they’ve changed up the colors to focus on more sophisticated navys, reds and blacks instead of the then-popular palette of acid green and mustard yellow, says Bryant.

Fabrics have stretch and are more lightweight, and the design has to consider comfort.

“We have a totally different way of thinking and getting dressed,” Bryant says. “Sixty years ago, there was a different code of what was presentable. There was no going out of the house without stockings, pantyhose, slips and garters, and long-line bras. Now you go out of the house in sweat pants.”