Grizzly Bear Smashes Glass Window at Minnesota Zoo The exhibit is closed until a new barrier is put up.

 -- Bear-proof glass was put to the test Monday at the Minnesota Zoo.

It failed.

One of the five layers of glass at the grizzly bear exhibit at the zoo in Apple Valley, Minnesota, broke yesterday morning when a bear smashed it with a rock, an official told ABC News today.

“One of the bears had a rock about the size of a basketball and managed to break one of the windows,” the zoo’s director of animal collections Tony Fisher said.

“At no time was there any danger of the bears getting out since there were still four layers of glass, but we’re not going to trust it,” he added.

The exhibit — home to three grizzlies that were orphaned in Alaska — is temporarily closed until the zoo can place a new bear-proof barrier in front of the broken panel.

Fisher said there’s no way to know for sure which bear broke the barrier.

“We thought we had all the rocks out of their exhibit but one of them dug it up somewhere,” Fisher said.

The zoo plans to custom-order a replacement glass piece, which could take up to several weeks, according to Fisher.

The 2 ½-inch-thick glass is similar to a car windshield and is designed to absorb impact.