Spanx founder Sara Blakely introduces new athleisure wear

The shapewear company Spanx was formed in 2000 by then-29-year-old Sara Blakely. While selling fax machines as her day job, Blakely used scissors and a pair of pantyhose to craft an undergarment that made her pants look more flattering.

Over 15 years later, Spanx sells its array of tight-fitting products in over 50 countries.

"I was so inspired to make a better and more comfortable undergarment that worked under my clothes," Blakely said on "CBS This Morning" Thursday. "I kind of think of my clothes as art, and if you're an artist, if you don't have the right canvas, it affects the building."

But while activewear sales jumped 8 percent in 2014, shapewear sales declined 3 percent, according to the market research firm NPD Group. Now, Spanx is getting in on the trend of athleisure apparel by expanding beyond its traditional undergarment.

"All of the technology that I was putting under, fabrics have advanced so much, yarns are so much better - we can infuse the shape right onto the clothes," Blakely said.

The company's new products - the EveryWear pants and the Lounge-Hooray tanks, shorts and more - come in more colors and shapes to stress comfort for everyday wear.

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"I'm a mom of four, and I also work, and so I'm running around and I didn't want to not be in my gym clothes because they were so comfortable, so the idea is -- how do you merge the gym clothes, the yoga pant that I always want to wear, with something that I can transition?" Blakely said.

The fashion consumer market is also changing. According to ChicagoNow/Waypoint Partners, 23 percent of millennial women between the ages of 15 and 25 would rather be more comfortable and less stylish. But Blakely said this specific demographic was not behind the brand's expansion.

"I just love the product, and I want to make the best possible product, and Spanx today is about options and celebrating all these options..." Blakely said. "I have different consumers who want different things out of Spanx."

But the brand has also received some pushback from critics who associate the company with encouraging a negative body image by giving off a message that women must fit a certain mold.

"You know what I say? Then don't buy them. It's fine. As a woman I'm just so happy that I had the option for Spanx because it opened up my wardrobe," Blakely said.