A cultural studies academic suggests that, simply by wearing cardigans, America's first lady is inverting a stereotype that has dogged public servants for decades.

The University of Sydney's Prudence Black will address a Melbourne conference today on the history of the garment, as worn by government workers.

She traced the cardigan's 19th-century origins, as clothing favoured by manual workers - ''tradespeople, fishermen, in fact anything but a desk job'' - to its ubiquity among bureaucrats in the 1960s. Today, the word cardigan remains a pejorative term used to describe an ineffectual public servant. Wearing one can connote a laidback work ethic, stemming from the outdated notion that a public servant has a job for life.

''There's this idea that having the security of a government job allows a relaxed manner in regard to dress codes, and this in turn allows an informality of dress,'' Dr Black said.

However, some attitudes are shifting, thanks in part to Ms Obama, who regularly wears the maligned clothing at important historical events.

She even wore a black cardigan on the night her husband won the 2008 presidential election.

Dr Black said, ''I love the way she wears them: she pulls the sleeves up, as though she's saying: 'I'm ready to work.'

''There's a physicality about the way she wears it; it's no-nonsense and practical … You can't imagine Julia Gillard or Margaret Thatcher in a cardigan.''

Dr Black noted a recent trend in some workplaces, such as law firms in Sydney and Melbourne, towards more conservative dress and grooming codes.

Even Canberrans knew not to wear a cardigan in Parliament, she said.

However, Dr Black hoped public servants' love of the garment would not succumb to the weight of old, negative stereotypes.

''That would be such a shame, because they're so comfortable and so useful.''

Dr Black will speak today at the Institute of Public Administration Australia's conference, which, among weightier issues, is exploring workplace fashion.