Tim Gunn says he loves the American fashion industry, but the Emmy-winning co-host of "Project Runway" said he is baffled by the way plus-size women have been ignored.

"It's a puzzling conundrum," the design educator and author wrote this week in the Washington Post.

Gunn cites new research from Washington State University that the average American woman now wears between a size 16 and a size 18. There are 100 million plus-size women in America and they have spent $20.4 billion on clothing, up 17 percent from 2013.

But many designers, Gunn said — “dripping with disdain, lacking imagination or simply too cowardly to take a risk” — will not make clothes for them.

According to a Bloomberg analysis, Gunn writes, only 8.5 percent of dresses on Nordstrom.com in May were plus-size. At J.C. Penney's website, it was 16 percent; Nike.com had just five items.

Gunn said it was “a horribly insulting and demoralizing experience” to shop with plus-size women.

“Half the items make the body look larger … Pastels and large-scale prints and crazy pattern-mixing abound, all guaranteed to make you look infantile or like a float in a parade.

“It’s mind-boggling.”

Even though Ashley Nell Tipton won this season's "Project Runway" contest with the show's first plus-size collection, Gunn said the breakthrough "managed to come off as condescending."

“I’ve never seen such hideous clothes in my life,” he wrote. “Her victory reeked of tokenism.”

Gunn said he was told by one judge that she was “voting for the symbol.”

“I wouldn’t dream of letting any woman, whether she’s a size 6 or a 16, wear them,” Gunn wrote. “A nod toward inclusiveness is not enough.”

Gunn believes designers and merchandisers could “make it work” for plus-size women, but concedes they are dragging their feet.

“The overwhelming response is, ‘I’m not interested in her,’” Gunn wrote.

“There is no reason larger women can’t look just as fabulous as all other women,” Gunn said. “The key is the harmonious balance of silhouette, proportion and fit, regardless of size or shape.”

Despite the financial potential of the plus-size market, Gunn said many designers are avoiding it.

“It’s not within their vocabulary,” he said.

But Gunn added that designers need to drop the trends that were established decades ago. Plus-size women are a viable part of the retail market.

“This is now the shape of women in this nation, and designers need to wrap their minds around it,” Gunn wrote. “I profoundly believe that women of every size can look good. But they must be given choices.”