One home with 4-foot-tall weeds, a sagging porch, and broken or boarded-up windows becomes two, which spreads to four and soon a whole block is falling apart.

Mortgage backer Fannie Mae is hoping to combat that ill with a new program that may eliminate plywood board-ups, by helping to pay for an alternate covering. It announced in early November that it will reimburse owners of vacant properties for the cost difference between the cheaper plywood and a polycarbonate material known as clearboarding. The latter looks like glass but is made of the same plastic as airplane windows (polycarbonate is a generic term referring to many types of plastic).

Companies that install polycarbonate windows say that the clear option helps secure the property, prevents criminals from hiding inside — and keeps the outside looking more attractive.

Fannie Mae had previously announced that it would use clearboarding on any post-foreclosure properties it controlled; the new deal gives banks still going through the foreclosure process the choice to use clearboarding with no additional cost.

“That is definitely their preferred method,” says Robert Klein, co-founder of clearboarding company SecureView, who spent 27 years in the industry boarding up foreclosed buildings on behalf of mortgage lenders. “I’ve seen what plywood does.”

Some communities have moved away from plywood entirely. The city of Phoenix announced in 2015 that if city crews moved to secure a property, it would no longer use plywood, shifting to polycarbonate.

“From my point of view,” says Klein, “I’m the one who boarded millions of properties with plywood. Boarding your property with plywood is an announcement: ‘My property is vacant, come and vandalize me.’ Immediately the value of the property next door is reduced by 20, 25 percent.”

Studies have shown that abandoned buildings are correlated with an increase in crime. Alan Mallach, a senior fellow at the Center for Community Progress, points to three reasons: First, the abandoned buildings themselves are used directly for crime. Criminals use vacant properties as a headquarters for everything from drugs to prostitution.

There’s also the broken windows theory, which signals to potential criminals that there isn’t a strong force in the neighborhood watching out for misdeeds.

And finally, vacant properties “serve as a signal to people who live here that the neighborhood is getting worse and it’s time to get out, or to people thinking about where to buy a house, that ‘this isn’t the place I want to be if I have any choice in the matter,’” says Mallach.