The one question posed to every celebrity on the red carpet has always been - you've guessed it - "Who are you wearing?"

But these days, entertainment reporters should be swapping the interrogative pronoun to "what".

That's because red carpet style is slowly going green, and we're not just talking about the season's penchant for emerald hues.

Thanks to Livia Firth, eco-campaigner and wife of the Oscar-winning Colin Firth, celebrities have been sporting strange but sustainable materials on the glitziest red carpets.

Mrs Firth launched a Green Carpet Challenge in 2009 to encourage designers to create one-off red carpet looks for her celeb friends.

She herself wore, not miles of gossamer-light tulle or - heaven forbid - fur to this year's Golden Globes, but an Armani gown made from recycled plastic bottles.

Since then, Meryl Streep has worn a gold draped gown made from eco-certified fabric by Lanvin;

Julianne Moore sported a Tom Ford cocktail dress made from fabric recycled from a vintage dress (which was, aptly enough, a shade of absinthe green);

and Viola Davis wore a salmon-pink Valentino gown which was also made from recycled plastic bottles to the British Academy of Film and Television Arts Awards (Baftas).

So it was more than timely that, last week, retail heavyweight H&M launched an eco-friendly red carpet collection made from organic cotton and hemp, and recycled polyester.

The Swedish chain store has worked with Hollywood stylist du jour Elizabeth Stewart, whose client list includes Julia Roberts and Cate Blanchett, on the Exclusive Conscious collection, a posh extension of its three-year-old Conscious line of sustainable clothing (a floor-grazing gown with plisse meringue skirt, for example, is going for $549).

H&M is the biggest user of organic cotton in the world, and was the first retailer to introduce garments made of organic hemp.

"For H&M, sustainability is a natural part of doing business in a globalised world and we look to making our products more sustainable on a daily basis," says Lisa Chai, PR and marketing manager for H&M Singapore.

As expected, celebrities such as Michelle Williams and Kristin Davis were clamouring to wear the upmarket looks from the label, better known for its affordable, fast fashion togs, thanks to its eco cred.

But such high-profile eco-fashion launches lead cynics to wonder, are retailers jumping on the green bandwagon just to grab headlines?

According to local environmentalist and green publicist Olivia Choong, long-term efforts from brands are true indicators of their commitment to saving the earth.

"Fashion brands should steer away from making eco collections a one-off event, as it comes across as gimmicky and opportunistic," says Choong, who founded environmental networking and information sharing group Green Drinks, and recently launched a campaign to raise awareness of chemicals in skincare and cosmetics.

"If businesses really want to help the environment, they need to look at greening their supply chain, materials, product life cycle, and using their brand as a vehicle to communicate environmental messages."

For founder of organic cotton casual fashion brand Etrican, Dragos Necula, the more lavish eco-fashion offerings of late reflect a shift in mindset:

While green fashion may have been started by environmentalists who were focused on the ethos of the movement, and not necessarily aesthetics, eco-fashion today is highly sophisticated and trend-driven.

"It became trendy to talk about eco products and responsible living and of trendsetters like celebrities and high-end designers who pick up on it," says Mr Necula.

"In addition, committing to working with eco-friendly materials is challenging and can quickly become an expensive undertaking because of the limited supply. This is why we are now mostly seeing higher-end, more expensive eco fashion lines emerging."

Luxe brand Stella McCartney, for example, is also a certified carbon neutral company and doesn't use leather or fur; while Burberry has adopted animal welfare guidelines, closely monitors its exotic skins supply chain, and supports efforts to improve transparency in the leather industry.

And the upmarket eco-fashion trend isn't just limited to frou-frou eveningwear.

One designer known for her sophisticated, avant-garde designs for men and women admits that it's been an uphill battle going green.

Berlin-based designer Esther Perbandt, whose pre-Spring 2013 collection will be available here from May 17 on digital trunk show portal www.futurefashionnow.com, tried to adopt sustainable production practices and materials three years ago, after participating in a programme which had designers from Copenhagen and Berlin try to find their own sustainable fashion criteria through a series of seminars.

Rather than create just three "green" outfits as required by the initiative, she transformed 70 per cent of her collection into a sustainable range.

"I was also rather inspired by the idea that going green could serve as a marketing strategy and be good for business," explains Ms Perbandt in an e-mail interview.

"But after that one season, I realised that it was more difficult than expected, especially since my ambitions for my designs required more than what was available through sustainable sources."

Unlike other designers creating just one-off sustainable outfits, however, Ms Perbandt was determined to keep striving towards an environmentally sustainable business.

Today, about 80 per cent of her Spring/Summer 2012 collection is now environmentally sound.

"It is so much easier to start a brand with a sustainable concept as you work with the right calculations and price positioning from the get-go, after conducting market research on materials and conditions," she adds, while explaining that she has been absorbing the additional costs involved in going green and maintaining her prices.

Her cerebral and often androgynous styles are priced from 150 euro ($247) for a top to 550 euro for a dress and 600 euro for a jacket.

And, as much as upscale eco fashion adds a much-needed dose of glamour to a niche industry, Mr Necula reckons that the focus should be on affordable green clothing that is accessible to the masses.

"As it gains popularity and more customers start buying into the concept, the supply and range of eco-friendly fabrics will increase, more designers will jump on the bandwagon and prices will come down. As a result, most people will eventually be able to afford it and eco fashion will become the standard, replacing fast fashion," says Mr Necula.

Because, at the end of the day, any style aesthete with a conscience would want to give a guilt-free answer to that all-important question, "What are you wearing?" on the red carpet, and practically everywhere else.

This article was first published in The Business Times.