Want to keep the planet and your portfolio green? The Fool shows you how in our special series on Earth-friendly investing.

Earth Day is probably the last thing on your mind when you think about disposable diapers and paper products.

But that's not how Procter & Gamble (NYSE: PG) and Kimberly-Clark (NYSE: KMB) want you to view their products.

Would you believe that disposable diapers are actually as green as their cloth counterparts? That's what a British study found when throwing the impacts of laundering cloth diapers into the mix. Many cloth-diapering advocates dismiss these claims as faulty, but P&G and K-C tout this as proof that their products are not as harmful to the environment as once thought.

P&G's 2012 goal is to deliver $20 billion of sales from products with "reduced environmental impact" while improving production processes to reduce waste. P&G says that it has already cut diaper weight by 40%, slashing diaper packaging by 70%.

Similarly, Kimberly-Clark touts the environmental friendliness of Huggies on its product websites. K-C seeks to improve its "green" standing by using recycled fiber in its Kleenex tissues products and cutting product packaging, according to its 2007 Sustainability Report.

"Green" disposable paper products (I know, it sounds like an oxymoron) aren't limited to diapers and paper towels. Even your coffee cups are becoming environmentally friendly, as International Paper (NYSE: IP) has developed biodegradable paper cups in conjunction with Green Mountain Coffee Roasters (Nasdaq: GMCR).

Most interesting, though, is that P&G states that only 5% to 10% of consumers are willing to buy a product solely because it's good for the environment, suggesting that P&G and K-C are making environmental initiatives a priority for altruistic reasons instead of real growth prospects.

But I'm not so sure this is all that true. TIME magazine recently reported that parents are moving toward cloth diapers, with cloth-diaper industry growth of 25% to 50% being driven by parents who are looking for an option they see as more environmentally friendly, not to mention cheaper. Green products really are everywhere: There are 43 million Google search results for "environmental product growth," and the first search result is actually for Bank of America (NYSE: BAC), touting paperless statements and environmental products and services.

The environmentalists and consumer products companies can argue about the true effects of disposable diapers, but it sure looks like green investing, not to mention that the trend toward improving products typically viewed as environmentally unfriendly, is here to stay.

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