You can use a sheet of plywood or even a flush door.

Some people had replaced the glass with sheets of plywood.

Early that morning we had seen a large, square, heavy plywood sheet.

The door had been glass, but a sheet of plywood was fixed over it.

Guy returned alone, and sat on a stool next to the sheet of plywood.

Doors are a better size than plywood sheets, and lighter as well.

There was a sheet of plywood covering the dining room window.

Each car looks like a torpedo with a big sheet of plywood on the back.

Here and there, though, plywood sheets still covered those openings.

Boy, just be glad it was only a sheet of plywood that hit your toe.