If Miuccia Prada's winter collection is hard to pigeonhole, that's the idea, the designer tells Susannah Frankel

"I was interested in working without any point of reference, without any idea, except to find something that looks new and modern to the eye." So says Miuccia Prada of her strangely beautiful autumn/winter collection. But, just in case anyone might think this was merely a one-season wonder, she adds: "For two or three seasons now, I've been doing that, working without any preconceived idea."

This may at least partly explain why, at first sighting, Prada collections have recently been more difficult than ever to pigeonhole; and why, for the past year or so at least, there's been no chance of pinning them down to a decade, say, or attaching them neatly to any of the, by now, tiresomely cliched fashion muses. Nancy Mitford, Marlene Dietrich, Josephine Baker... The list goes on and is about as inspiring as a walk in the rain.

"If you want to make something new, you need to make your mind blank and just look with your eyes, just judge with your eyes. That is much more difficult," Prada says. Certainly, the colour palette for the current Prada collection in particular has been described as everything from "clashing" to plain "ugly". The designer herself prefers to define the collision of charcoal grey, emerald green and turquoise, say, or of orange and dusty rose more thoughtfully. "I am looking at them now, those colours," she says, speaking from her studio in Milan, "and they look very beautiful. The colours are right for the moment, that kind of violent colour is right for now, but also sophisticated - and unusual."

At least part of the secret - and let's not forget that giving the world anything unusual fashionwise, particularly when at the helm of a globally recognised brand, is no mean feat - lies in a treatment of fabric that is far from simple. "The colours came out by superimposition," Prada confirms - pink over-knitted with black is just one example. "They look new because of the superimposition of the materials, and the fact that all the fabrics were treated at least two or three times."

If there is one word that appears to encapsulate the current mindset over at Prada HQ it is "mutation". "We mixed one fabric with another fabric, one colour with another colour, and so things became something else. The shapes themselves were relatively simple but then the shoe became the sock, the sock entered into the colour of the skirt..."

It is true that the silhouette is relatively uncomplicated at first sight, but what is remarkable is the fact that, in certain instances, it is slightly stiff, standing away from the body as opposed to clinging to every curve. "You know," Prada says, "one problem with fabric is that when it is really beautiful it is never thin. Thin fabrics are banal. You can't do anything with thin fabric. It is only when you work with thick fabric that you can introduce new ideas."

Thick fabric is, however, never likely to be as obviously flattering as more lightweight weaves - the teddy-bear coats and jackets included in this collection in particular are clearly hardly designed to emphasise the "perfect" size-zero frame.

"Yes," declares the high priestess of Italian style, "if you just want people to look thin and sexy, then you end up doing things that are just so boring that there is no possibility of invention. Everything is about super- tight jackets, super-narrow, constructed. I don't like them. I think that fashion should be more than just obviously appealing. A narrow sexy dress is so boring."

Thankfully for the world, this is a designer gifted enough to ensure that, while the fabric might not flow across the body like silk Charmeuse, the end result is clothing that, though neither conventionally hour-glass or strictly svelte, is still flattering.

"I know we live in a world where everyone wants to look thin," says Prada, "and, of course, in the end, it is a lot of work, but you have to go back to make your work more appealing. It's surely much more exciting to have something interesting to wear, and to have a sense of your own body in a new and different way."

Given that it is not news that a contrary streak runs through this great fashion designer's veins - and indeed, that there is nothing Miuccia Prada likes more than a challenge - it should perhaps come as no surprise that, while the current autumn/winter collection focuses on heavier fabrics, for spring/summer 2008, thin fabrics take centre stage, prompted by Prada's desire to make them more interesting.

It is, in the end, just this restless spirit that makes the Prada brand among the most exciting and innovative in the world today. The woman responsible for the design of it, however, is never easily drawn. In fact, Miuccia Prada is about as difficult to pigeonhole as the clothes she creates.

As she herself explains, by way of conclusion: "To think about and talk about my work is becoming more and more difficult all the time, but at the point when I was working on this collection, I was really fed up with everything, and also fed up with finding an idea or a title for my show, and of having to have something to say about my source of inspiration, for example. Let's just say I have nothing to say."