Fashion: What we hide reveals a lot about us: New York's Metropolitan Museum of Art is exposing the significance of what we wear under our clothes. Marion Hume reports

INTERNATIONAL fashion shows have been full of examples of barriers breaking down between what can and cannot be clothing. In Paris, London and on Milan's new-wave catwalks, what used to be called long petticoats turned up as dresses over shrunken sweaters and biker boots. Froth and flounces associated with lingerie came out on top as designers, in their attempts to find alternatives for the rigid armour of the power suit looked to what had been worn beneath it.

And for evening, the floaty little black lace and satin nightie has replaced the structure of the little black dress - or, in some cases, is being worn over it. Herve Leger's versions seen in Paris followed the exquisite example made by Balenciaga in 1957, when his baby doll dress had the body contained in a fitted carapace with a cage of black lace swinging over the top. This season, Karl Lagerfeld took the most unalluring element of men's underwear, the long john, and sent it out to be seen at Chanel.

So Infra Apparel, an exhibition currently at the Metropolitan Museum of Art in New York has a pertinence that makes it worth discussing with those who will not have the opportunity to see it. Richard Martin, the co-curator of dress at the museum, and Josie Natori, a Saint Laurent couture customer and purveyor of slips, petticoats and cami-knickers under the Natori label, are an unlikely team. But a chance meeting and a shared idea has led to what is probably the most interesting and challenging fashion exhibition currently showing anywhere.

Infra Apparel, which opened on Monday and runs until August, analyses the importance of underwear. Ms Natori has long believed it to be every bit as important as the clothes sometimes worn on top of it. Mr Martin, and his associate curator, Harold Koda, are fascinated by the visual messages in what we choose to show and what we choose to hide. The two men, who joined the Met in January, follow in the august tradition of the late Diana Vreeland, who staged such memorable exhibitions at the museum that she can be credited with helping to change the way fashion is viewed by academia worldwide. Post- Vreeland, fashion in the collections of establishment institutions became as important as painting, sculpture or Egyptology to indicate social change and the preoccupations of its time.

Nothing is as revelatory in clothing terms as what we choose to display and what we cover. 'Underwear,' says Mr Martin, 'has sought with fascinating persistence to convey elements of bedroom privacy to the public domain.' Madonna's deliberately shocking soft boudoir pink, Valkyrie- breasted corset is the most obvious example of the powerful punch that sultry satin and lace can pack when they become visible. But Madonna was not the first to express female liberation by showing what was created to be concealed; in 1783, Marie Antoinette chose to be depicted in her 'chemise a la Reine' as a protest against the rigid rules of the French court.

Mr Martin and Mr Koda wanted a debut exhibition that would grab attention. The word got round that the Met was showing sex, and certainly some of the clothes, such as Thierry Mugler's dominatrix laced dress and Azzedine Alaia's revealing slips of carefully constructed nothingness have an erotic charge. But the larger significance concerns the cross- fertilisation of the intimate and the social.

Ms Natori's involvement is as sponsor, making the exhibition possible. In her 15 years in the upper end of the lingerie business, she has been persistently approached by women at parties who whisper like conspirators that their satin palazzo pants are in fact a pair of pyjamas, that the hint of silk under their jackets is a petticoat. 'I long ago thought why shouldn't underwear also be clothes. Now the bodysuit is seen as often as the blouse,' she says.

Infra Apparel also charts Lagerfeld's cunning continuation of what Coco Chanel started when she took the jersey fabric of men's underwear and made it into easy clothes for women. When Marlon Brando appeared in a sweaty vest in A Streetcar Named Desire, it caused shock waves. A modern Chanel evening dress of pristine white vest with crossed CCs and a black tulle skirt is, say Mr Martin and Mr Koda, 'a tank-top worthy of Stanley Kowalski combined with a skirt fit for Blanche DuBois'.

The exhibition analyses what can happen when clothing chooses to expose its foundations and techniques. A cocktail dress by Bill Blass celebrates the pin-tuck construction of underwear, yet no longer looks even remotely unseemly. In contrast, a tattered sweater by Martin Margiela deconstructs what is usually kept hidden by putting it on show. The sweater is made from men's socks, with the original heel sections forming elbows and shoulders. The effect is as ugly, as challenging and as shocking as some people find the outfits Madonna uses to express herself.

(Photograph omitted)