Just how 'green' is that shirt?

Prove it! That's how consumers ought to respond when presented with "guilt-free, socially responsible" products.

Spurred by consumer interest (and "green" profits), retailers now fill their stores with everything from No Sweatshop garments to sustainable timber. You can feel good about buying a T-shirt made without using child labor, or in purchasing ecofriendly detergent, fair-trade coffee, even "responsible" jewelry.

But judging competing social and environmental claims isn't so easy, and the task is getting more complex now that companies like Britain's Marks & Spencer are taking on climate change directly with a "carbon free" lingerie factory in Sri Lanka promising a garment produced entirely with renewable energy.

Yes, "green lingerie" is here, but should the retailer emblazon the item with a "carbon free" label and expect consumers to fully understand and accurately evaluate – let alone be receptive to – purchasing such a product?

Just how "green" is that shirt, dress, or blouse?

True sustainability requires independent certification, extensive consumer-education campaigns, and a desire and ability to review entire supply chains, say environmental authorities such as Linda Greer, a Natural Resources Defense Council senior scientist who specializes in toxic chemical pollution in textiles production.

"How do I know if a garment is 'green'?" asks Ms. Greer. "The answer is, there's no way to know that. Even if you buy a T-shirt that's organic, you don't know the factories and the chemicals that went into dyeing it, or how much carbon they emitted into the air."

An article of clothing may be made with organically grown cotton, but it's at the processing stage – often involving coal-fired boilers and poor treatment of waste- water – where garment producers create the biggest carbon footprint.

By this measure, the Sri Lankan lingerie factory – strictly a cut-and-sew operation – is a relatively manageable undertaking on the front end of a supply chain that has yet to be fully vetted.

Progressive retail players like Marks & Spencer, Adidas, and Nike are well on their way to improving raw materials cultivation, with organic fibers and recycled plastic waste for polyester and fleece products a few of the sustainable practices now being mandated.

But there isn't a mass retail company that has developed a full sustainability standard that accounts for the garment across every step of production.

"No one has done that," says Mike Barry, head of corporate responsibility for Marks & Spencer. The retailer will not be slapping a "carbon free" label on its new lingerie line, confirms Mr. Barry.

With more than 35,000 product lines bearing unique carbon footprints, the cost to Marks & Spencer would be enormous – if indeed the labeling were to be rigorous and accurate.

"Even if we spend $5,000 on each label," says Barry, "it's going to cost a lot of money to give information to consumers who may not be ready to act on it. So a carbon label might be a part of the solution in the future, but not tomorrow."

Consumer rejection is one of the main hurdles, says Marsha Dickson, chair of the University of Delaware's fashion and apparel studies department.

"Labels on underwear are small," notes Professor Dickson, "and that's tricky because the tendency then is to boil it down to a simple message. With the environment, there are so many ways it can be impacted in textiles and clothing. They'll have to be real specific in the standards they're trying to meet and it will have to be traceable and verifiable."

The carbon-neutral task is so massive that Marks & Spencer has taken to "hot spotting" – the term Barry employs when discussing the 100 priority commitments the company has outlined in its ambitious Plan A initiative, which includes aiming to make the company's operations in Britain and Ireland carbon-neutral by 2012.

High on this list are "green" manufacturing units and the idea that the first one in Thurulie, Sri Lanka, can serve as a blueprint for others to follow.

The Thurulie ecofactory is owned by MAS Holdings, a powerhouse apparel manufacturer with more than 45,000 employees and 2007 earnings approaching $700 million.

It cost MAS $7 million to build the ecofactory – roughly 25 percent more than a conventional one. For small- to medium-size enterprises, that figure will be an intimidating barrier.

Apart from Marks & Spencer "sponsoring" the architects' design costs, the ecofactory was paid for entirely by MAS – and without any increase in the purchase price of the lingerie made.

Its design – reviewed this past month on a tour with MAS officials – integrates evaporative cooling technology, solar panels and hydro power, with energy-efficient task lighting, low-emissivity glass (which cuts down on heat transfer), and traditional applications such as courtyard design and tree plantings.

But going ethical will eventually cost the consumer more at checkout, warns professor Dickson.

"We pay less and less, from a consumer standpoint, and yet more and more demands are being placed on suppliers to respect labor rights and the environment," says Dickson. "This takes significant investment in [factory] plants and human resources."

How is MAS able to justify making such a substantial up-front investment?

Economies of scale is one answer but so, too, is the fact that MAS will save money on rising fuel costs while better positioning themselves to compete for green-conscious retailers and consumers.