NEW YORK – It’s the perfect fit.

Two of the world’s top bra makers are coming together in the biggest development in the $11.5 billion underwear industry in years.

Hanesbrands, which makes the Wonderbra, said Tuesday that it agreed to buy bra and underwear company Maidenform Brands Inc. for about $547 million. The deal would add brands like Maidenform, Flexees and Self Expressions to the Hanesbrand roster that includes Playtex, Bali, Champion, Wonderbra and its namesake Hanes.

The merger comes as traditional bra and underwear makers are facing tough competition from specialty stores such as Victoria’s Secret that focus on frilly designs and newer rivals like Spanx that make shapewear that promises to control and smooth out bulges.

“Maidenform has great brands that consumers trust,” said Hanes CEO Richard A. Noll. “Combining the complementary strengths of both companies creates a lot of growth opportunities.”

Bras, which are as much about fashion as they are about function these days, are the biggest sellers in the intimate apparel arena, making up about 48 percent of all sales, according to research firm IBIS world. Panties make up about 24.8 percent of sales, sleepwear makes up about 22 percent and shapewear 5.2 percent, according to IBIS figures.

The bra and underwear industry has growth spurts when new trends come along. Think boy shorts three years ago, for example, or shapewear over the past two years. But when it comes to what they’re wearing underneath their clothes, Americans have cut back on their shopping habits since the recession.

“It used to be women invested in their intimates, now they’re investing either in their bra wardrobe or panty wardrobe,” said Marshal Cohen, chief industry analyst with The NPD Group. “The economy changed the way we buy; we’re not buying everything all at once anymore.”

The industry has been playing with sizing in recent years to get growth. From 20 sizes 20 years ago, there are now more than 90 sizes, said Kate Terhune, marketing manager for Intimacy, a chain that specializes in helping women find the right size undergarments. And HanesBrands said Wednesday that Maidenform’s average-figure bra business will complement its full-figure bra collection.

Ninety-one-year-old Maidenform was a pioneer in the bra industry in the 1920s, patenting the first modern-seamed “uplift” bra in1925. But the Iselin, N.J. has been suffering from losses, hurt by tough competition in the shapewear business and lower sales from department stores, where Maidenform products are traditionally sold.

The company said it has been evaluating its strategic options. Maidenform CEO Maurice Reznik said that the deal was appealing in part because it provides the necessary infrastructure and resources to help grow its business.