They say necessity is the mother of invention.

For Heather Knox, it was frustration that drove her.

After spending years having to wear two bras at once to support her 36C breasts, she came up with the idea of combining a push-up bra with a full coverage one. And in 2006, she applied for - and got - a patent for her "multi-layer uplift bra."

Yesterday, she filed a federal lawsuit against Victoria's Secret and its manufacturer, claiming that the new BioFit 7-way bra infringes on her patent.

A spokeswoman for Victoria's Secret's parent company, Limited Brands Inc., which is also named as a defendant, could not comment on the pending litigation.

In the lawsuit, Ms. Knox, of Monroeville, Allegheny County, claims that the BioFit bra only infringes on her patent in its larger D and DD sizes, where it features what the company calls "power mesh."

"It's scary to go up against a big company, but I think in the end, the right decision will be made," said Ms. Knox, of Monroeville.

Her search for the perfect bra goes back years.

With a push-up, Ms. Knox said her breasts would go up and over the cups. But with a full-coverage garment, she looked saggy.

She wore both at the same time to try to counteract each other.

"I'm a 36C. I'm not a GG or anything," she said. "I'm 40. Gravity has taken its toll on me. Even at 30, gravity had taken its toll on me."

But in early 2001, Ms. Knox, who works in the insulation and energy conservation field, hit upon her idea.

She went to the Carnegie Library of Pittsburgh and did patent research to see if something like what she envisioned already existed.

It did not, so she made her way to a local patent attorney. She began the process, but was sidetracked after she lost her job following the Sept. 11, 2001, attacks.

But three years later, she rekindled her interest and filed the paperwork.

In 2006, she was awarded a utility patent.

The process of getting the patent and trying to license her bra has cost Ms. Knox about $12,000.

"I believe in it," she said.

She figured if she had the problem finding the right bra, that other women have likely encounter it, as well.

Her bra, Ms. Knox continued, gives a woman "the lift necessary to counteract gravity, and the other piece helps hold it against your body so you have a nice, smooth silhouette."

She has contacted a number of companies to license her design to no avail.

"With bras, it's a huge quantity you have to manufacture," she said. "Five or 10,000 in each size and each color."

And Ms. Knox was having trouble finding someone who could simply make her a prototype.

She even attended trade shows, and went to auditions for "American Inventor" in New York, and to a search for Oprah's Next Big Idea show in Philadelphia.

In January 2007, she got in touch with the head bra designer at Victoria's Secret. She spoke with the woman on the phone and sent her an e-mail, including a description of her bra. She noted in the e-mail that the design was patented.

She never heard anything back from the popular lingerie company. But then recently saw the BioFit bra.

"It's been very hard to license as an individual," Ms. Knox said. "And these big companies don't make it any easier."

Charles Von Simson, the patent litigation attorney representing Ms. Knox, doesn't believe Victoria's Secret actually sought to steal her idea.

"As long as it infringes a patent, it doesn't matter," Mr. Von Simson said.

Whether the infringement was willful could have an effect on any damages Ms. Knox might collect at trial, but it has no bearing on the actual violation.

"The industry is very sloppy, and people do rip each other off all the time," Mr. Von Simson said. "Part of that is because a lot of people don't enforce their rights because it's just too daunting."

Victoria's Secret has been marketing the new BioFit 7-way bra extensively, Mr. Von Simson said.

He believes Ms. Knox has a strong case.

"If you're a patent holder, you have a very strong set of rights," he said. "It does put individual inventors on a strong footing up against these big companies."

Paula Reed Ward can be reached at pward@post-gazette.com or 412-263-2620.