Jacobs was awarded a US patent in 1914 for her innovation that held breasts up from the shoulders and separated the bosom into two individual shapes. While there is some debate about the inventor of the brassiere, with some claiming it was 18th-century French corset-maker Herminie Cadolle, the curator of fashion and dress at Sydney's Powerhouse Museum, Glynis Jones, says Jacob's design is the basis of the modern bra and a $30 billion industry.

''People had been experimenting with bras before that but we remember her because she really created the bra that separated the breasts and took out a patent.''

Jacobs sold her patent for $1500 and the company to which she sold it made more than $15 million in the next 30 years. Mass-produced for the first time, women could wear a soft, lightweight garment that separated the breasts.

World War I helped cement the bra's popularity, after women in Britain and the US were asked to give up their corsetry to free up metal - in the US alone it saved 25,000 kilograms, enough to help build two battleships for the allies.

The dress collection at the Powerhouse Museum has more than 100 bras, the oldest is a ''bust improver'' and Jones says the evolution of the undergarment over the past 100 years is all about the silhouette, with technology driving changing fashions.

The Edwardian silhouette was a sinuous S: with a large bust and bottom - the ''bust improver'' facilitated that shape.

''It's like a bandeau and it's made of linen, has boning and laces [that] go through the front of it and you can pull on the laces and it creates a shelf across the front against the breasts, so that it extends the breasts. But it doesn't separate them, it creates this mono-bosom, which was very popular with Edwardian dress.''

Every woman remembers her first brassiere - it's a right of passage but also a fashion statement, from the bust-flatteners of the 1920s, designed to give women a boyish slimline figure, to the 1930s, when rayon became a popular fabric for bras as a nicer option than cotton and more affordable and practical than expensive silk.

''It meant that underwear became cheaper and there was a greater variety of styles available.''

In the 1950s, advances in sewing created whirlpool stitching, which in turn was responsible for ''torpedo-shaped breasts''. ''You had stitching that went to a point at the nipple and it really thrust the bust out and up and you get that form with Jayne Mansfield and Marilyn Monroe,'' Jones says.

The 1960s and 1970s were all about colour and matching sets. ''Getting a more useful range of garments, coloured prints and matching bra-and-pant sets. Underwear looks more fun.''

In the '90s, underwear became outerwear. ''Undergarments became so beautiful you could wear them on the outside and you get a lot of designers doing underwear.''

The Wonderbra was created in 1964, but in 1994 it really took off when model Eva Herzigova took her shirt off in Times Square and said ''hello boys''.

''The Wonderbra has 54 design elements: it lifts the bust and has a deep plunge so you can wear low-cut clothing, but it also brings the bust together. It gave women fuller form.''

In comparison, Jacob's original patent bra application had just eight design elements.

While the Wonderbra advertisement caused a stir in 1994, today parades of women in the underwear are commonplace.

Last year, model Alessandra Ambrosio walked the runway wearing the Victoria's Secret Fantasy Bra - a $2.5-million piece called the Floral Fantasy because of its flower-covered design. The company has been making Fantasy Bras every year since 1996, but the 2001 brassier was its most expensive. Nicknamed the Heavenly Star Bra, it was worth $12.5 million, with 1200 Sri Lankan pink sapphires and a 90-carat diamond centrepiece worth $10.6 million. Fantasy Bras are part of the company's marketing strategy, because partially naked women are no longer enough to guarantee media attention. Only one of the million-dollar bras has sold and most are dismantled.

The annual parade of half-naked women that makes up the Victoria's Secret fashion show is broadcast to 185 countries and has a US audience of 9.5 million. It's leagues away from the first television advertisements for brassieres in 1954.

Playtex was the first company to to advertise undergarments on TV. ''At that time they weren't allowed to show live models on television but they could show the packaging and it wasn't until the 1970s that you were actually allowed to show live models wearing undergarments on TV,'' Jones says. In fact, Jones is on a search for a Playtex bra for the museum's collection.

But despite their cost and ubiquity, scientists are divided on the value of bras.

Sub-dean of the Canberra Clinical School and Professor of Anatomical Pathology at the Australian National University Medical School, Jane Dahlstrom, says a woman's breast size is partly related to our genes (including our height) and to our weight. Breast development begins in the womb from five weeks gestation.

''The breast is made up of glands, epithelial cells and stroma, mainly fat,'' she says. ''The glands grow in number during adolescence and get larger during pregnancy.''

With age, the amount of glandular tissue reduces, so breasts become more fatty.

Professor Dahlstrom says those changes can not be prevented, although hormone replacement therapy does reduce the shrinkage of the glandular tissue in later life.

''In a woman over 49 years, the density of the breast becomes less because there are less epithelial cells … so when you are very young and very old, most of your breast is made up of fat, but when you are in the prime of your life, you will have much more glandular tissue.''

Australian lingerie manufacturer Berlei has sponsored research on breast bounce. They found that during high-impact exercise, an unsupported 12B bust can bounce up to eight centimetres, and a 16DD bust can bounce up to 19 centimetres. But wearing a correctly fitted sport bra from the Berlei range reduced movement by up to 50 per cent and helped stop tissue damage.