ANAHEIM, Calif. — That black plastic lining sprayed on beds of thousands of pickups every year has gone to war — protecting everything from the Pentagon to Humvees.

The discovery of military applications is creating a nice sideline business for two pickup bed- liner companies: Line-X of Santa Ana, Calif., a chain of 560 truck-bed liner franchisees around the country; and Rhino Linings of San Diego, which has about 900 dealers in the United States. Both are privately held.

The companies have long known their spray-on polyure-thanes have more uses than pickup beds. Line-X, for instance, says its coatings cover the ground around oil storage tanks to contain spills and is used on Disneyland rides and submarine decks.

Now it's being used to coat buildings — most notably the Pentagon — as a protection from bombs. When sprayed on the masonry walls of buildings, it can reduce the disintegration of bricks or concrete into deadly flying fragments in a bombing or other attack.

The sideline took off after the Sept. 11 terrorist attacks, including the one at the Pentagon that killed 125 people who were inside the building when the plane hit, which underscored the need to protect people in buildings being attacked. "That really was our entry into this market," Line-X CEO Scott Jewett says.

Rhino president Pierre Gagnon says the military is his company's single largest customer, even though 60 percent of the business is still bed liners.

Both companies have had testing conducted in the New Mexico desert. Jewett says Line-X polymers passed tests in which 200 pounds of TNT were exploded 30 feet from building mock-ups. The blast broke through the building that wasn't treated with the bed liner. The treated room remained intact.

"It's good stuff," says retired Lt. Gen. Robert Flowers, former chief of the Army Corps of Engineers and now CEO of HNTB Federal Services, which provides contract services to the government. He says the search for materials to protect against fragmentation started after the bombing of the Khobar Towers in Saudi Arabia in 1996, which killed 19 U.S. military personnel.

A consultant working with Line-X to protect the Pentagon, Tod Rittenhouse of the design firm Weidlinger Associates, says the discovery of the polyurethane's potential for blast protection was almost accidental. "We were testing some general materials for how to hold brick walls together and someone said, 'I just had this stuff sprayed on my truck. Let's give it a ride,' " Rittenhouse says.

About 20 percent of the Pentagon has been covered. The remainder could take up to five years, Jewett says.

The material also coats the plates inside 50,000 bulletproof vests being issued to troops in Iraq and Afghanistan. The plates can protect wearers from a bullet fired from an AK-47 automatic weapon, Line-X says.

Rhino's polyurethanes are being sprayed on Humvees to reduce noise and help seal in the armor, which was added to protect against roadside bombs. A version is also being used to coat fuel tanker trucks in Iraq — the plastic forms a membrane that can help seal leaks, Gagnon says.