
The plans , Marc Jacobs' business partner, on Twitter.
He said that the brand was "in talks" about the range, as well as indicating that the plus-size clothes would be a new line rather than making the Marc Jacobs catwalk collection available in bigger sizes.
Duffy said: "Marc and I are building a brand. That's what we do. We will always have a collection line. But they rarely make much profit. As everyone knows."
Marc Jacobs has parlayed the admiration of fashion editors into global success by putting his name to a huge range of products from the usual perfumes and spectacles to key rings, hairclips and a range of pet accessories called Bark Jacobs. He also plans to open a bookstore called Book Marc in New York’s trendy Bleecker Street this winter .
The company’s Twitter feed is currently a hive of news and promotional activity. At the moment, the company plans to give away goody bags each week until 15 September. It is also working out the legalities of running a Twitter competition to let two people fly to New York and watch the Marc Jacobs fashion shows.
Duffy says he is only allowed to take control of the feed twice a year as he gives away too many prizes.
Fans of the designer are being asked to suggest names other than "plus size" to describe the new range, which should be available next year.
Most high-end fashion labels do not go beyond a UK size 14 when they manufacture their collections. Although there is demand from larger women for better clothes, designers argue it is harder to create well-fitted larger garments, as weight goes on different areas of the body.