You can saw it, you can sand it and, if you want to, you can carve your sweetheart's name into it. But beware: Mementos etched into this park bench won't last forever.

That transient quality is one of the main selling points of recycled plastic "lumber" — vandals can't touch it. Markers and spray paint can be sanded away, and the "woodworking" of idle teens can be melted off, and the reshaped lumber made to look as good as new.

Of course, the ultimate appeal of recycled plastic lumber is that it's not really lumber at all. Though it looks and feels like hardwood, that picnic table you're sitting on is really about 2,000 reconstituted milk jugs that never made it to the landfill.

"I certainly don't condemn the use of treated wood," said Bob Schildgen, a Sierra Club magazine columnist and "Hey Mr. Green" blogger. "Harvesting timber is not an inherently bad thing, it can be done in an environmentally sustainable way ... but I would still give a nod to recycled lumber for the maintenance and material that would have been wasted."

Many people do. Since the late 1980s, recycled plastic lumber has made gains on its hardwood counterparts on mostly "greenness" grounds.

"Obviously, a tree is a renewable resource," says Alan Robbins, owner of The Plastic Lumber Company, Inc., in Akron, Ohio. "There certainly are a lot more trees than there are milk jugs in the environment. But a milk jug is a very stable part of the economy — they're not going away."

Robbins got into the business almost 20 years ago, about the same time chromated copper arsenate, the wood preservative that gave industrial-strength timber that certain greenish tinge, was either banned or replaced voluntarily throughout the preserved-wood industry after arsenic was linked to certain cancers.

"It's been a crazy ride ever since," Robbins told FOXNews.com.

"[Plastic lumber's] market acceptance has been so total that it is very difficult to find any natural wood used in current construction projects in park and playground applications," he wrote in a 2007 report on the industry, though he noted that the housing bust was starting to hit home.

Recycled plastic lumber comes in your standard 2x4 and 4x4 planks, but can also be molded into 3-D shapes and curves unseen on the woodcutter's block. It can be sawed, screwed and sanded just like wood, but without the sawdust.

A grain texture can give the surface a more woody appearance, and it's available in many different "flavors" — redwood, cedar, mahogany, "weatherwood" and even "night glow," which is phosphorescent and intended to hold up road signs.

It's most often used in park furniture, hot tubs, decking and railings, signs, railroad and marine applications and the birdfeeder industry.

"'No painting, no splinters, no rot' seems to be the catch phrase," said Robbins.

The Environmental Protection Agency is now warming to 100-percent post-consumer plastic lumber, reporting that the products last longer — indefinitely, at this point — and cost less to maintain than regular wood since they're impervious to termites and are flame-, weather- and vandal-resistant.

But not everyone's jumping on the recycled-plastic bandwagon. Plastic lumber, which costs three times as much as some wood, may be more susceptible to warping and discoloration and can melt under a tabletop camping grill. It's also more likely to sag under a heavy load.

And, like the old plastic or paper quandary, the jury's still out on which lumber is "greener."

No comprehensive study has yet compared the life-cycle energy consumption of real versus plastic lumber, according to the Madison, Wis.-based Forest Products Laboratory.

There are two major "species" of recycled plastic hardwood. The most prevalent is made of high-density polyethylene — derived from milk and juice jugs.

The other comes from recycled polyvinyl chloride — the notorious PVC that Greenpeace dubbed "the single most environmentally damaging of all plastics." Dioxin, a carcinogen and immune suppressant, is a by-product of vinyl production, as are many tons of greenhouse gases.

"The energy used in the manufacture of plastic and plastic wood composites is much higher than that used for manufacturing solid wood products," Dr. Brian Bond, a professor at Virginia Tech's Department of Wood Science, wrote in an e-mail exchange. "And many plastic wood composites still require a percentage of virgin plastic."

The Healthy Building Network suggests buyers steer clear of fiberglass-reinforced "composite" lumber, even though these more rigid products lend themselves better to structural applications.

The EPA warns that, because composites are non-recyclable, "a growing plastic lumber market could actually increase plastics production and waste volumes."

The promotion of plastics recycling in general boosts the production of virgin plastics, according The Healthy Building Network. But manufacturers argue their production line is greener than other kinds of recycling.

"It is mechanically ground, then it goes through a wash process," said Brian Larsen, owner of Bedford Technology, LLC, a Minnesota-based manufacturer of recycled plastic furniture, speed bumps and marine pilings. "It changes state — kind of like water, it melts and then it refreezes again," he said, adding that there are no heavy chemicals used, and no by-products.

He also said that since HDPE is so heavy, it's not economically viable to process overseas. Most plastic lumber is therefore "grown" locally, shrinking its carbon footprint.

And even though it comes from non-renewable petroleum, the volumes of milk jugs diverted from landfills keeps the consciences of plastic lumber builders clean and green.

"We're recovering that product and turning it into something else," said Robbins. "A dairy bottle with a [two-week] life in the fridge can be turned into an infinite life for long-term use."