In 2009, James Reinhart was standing in his closet. It was full of clothes, but he didn't feel like wearing any of them. 

That moment was the beginning of ThredUp, a fashion-consignment website with almost 1 million customers and more than $48 million in backing from financiers, including Trinity Ventures, which helped Starbucks get going. Basically, it's a middleman for people looking to buy or sell high-quality used clothes—and one of a range of start-ups catering to the swelling wave of people taking to the cloud to buy, sell, give, get, or rent secondhand apparel.

Considering that the average American throws away 68 pounds of textiles each year, and that a single cotton T-shirt takes 700 gallons of water to produce, and that 80 percent of items Americans own get used less than once a month, these types of sites are looking increasingly attractive to families concerned about both their environmental impact and their finances.  

To get started on ThredUp, you order a free polka-dot plastic bag, fill it with clothes you're tired of, and send it back (also for free). ThredUp's employees sift through your castoffs, post what's good—you get part of the proceeds when one of your pieces sells—and send the rest to a fabric recycler. Though Reinhart started ThredUp primarily to make money, his burgeoning business has diverted more than 1.5 million pounds of textiles from landfills since 2012.  

Yerdle works a bit differently: It helps people give away things—clothes, mostly—that they no longer want. It's free to claim a "Yerdled" item, except that you have to pay a nominal shipping fee (usually $2), and credits get deducted from your account—credits you earn by listing your own stuff to give. Items posted on Yerdle are often gone within 30 minutes. 

"People have gotten super-good at buying things: It's so easy to go to Amazon and order, or to go to Walmart and see what's on sale," says Rachel Barge, a Yerdle spokesperson. "But there's not a good way to get value from those items after you've bought them—you can't sell them for much on Craigslist or eBay." 

Yerdle was cofounded by Adam Werbach, a former Sierra Club president. Its mission is to put the $5 trillion worth of durable goods gathering dust in closets and garages to use. At 150,000 users, the Yerdle community is still relatively small. But it's catching on. 

"People tell us, 'I used to shop at Target seven days a week, but now I use Yerdle and I'm addicted,'" says Barge. "They're also really excited about giving things away. And you're rewarded for this behavior. We call it a 'currency of generosity.'" 

You don't have to be an altruist to use Rent the Runway, a company whose more than 50,000 designer dresses are available to rent for a fraction of what they'd cost to purchase.

Buying a new Badgley Mischka sheath, for example, will strip you of $940, even though you might wear it only once or twice. Via Rent the Runway, you can have it for four days for $45, plus modest shipping and insurance fees. 

"We've entered a world of fast fashion where you buy a lot of clothes and they don't last all that long," Barge says. "If we can share our fashion, it's great for the planet. If you want a new outfit, new-to-you is almost as good as brand-new." 

Photo courtesy of ThredUp