Green is the insulating gas that goes into the double wall.

It had a double wall and was almost impossible to escape from.

"While we were looking for you, chief, he'd have had plenty of time to get down through a double wall and into the library."

The first step was building a double wall for fortification purposes.

The base of the triangle was protected by a double wall and a pit.

That was when they were finishing construction of the double walls.

The inner walls are a double wall, with a military road in the middle.

This is an old castle, and it probably has double walls.

It would be encased in concrete, deep within the building's double walls.

A translucent double wall was designed to receive an important collection of objects given by the population.