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 worn 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. And wearing one can connote a laidback work ethic, stemming from the outdated notion that a public servant has a job for life.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.

"If you're characterised through the stereotype of cardigan- wearing, it can mean you're out of date or stuck in your ways."

However, some attitudes are shifting, thanks in part to Ms Obama, who regularly wears the maligned garment at high-profile 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 said the cardigan was the worker's friend: practical, as it could be thrown in a bag or over the back of a chair, or worn after work to "dress up" an outfit.

But she noted a recent trend in some workplaces, such as law firms in Sydney and Melbourne, towards more conservative dress and grooming codes. Even Canberrans know not to wear a cardigan in Parliament.

However, Dr Black hoped public servants' love of the garment will not succumb to the weight of an old, negative stereotype.

"That would be such a shame, because cardigans are 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.