He would have staked his life on the fact that those scales were virtually impenetrable.

Much of it is also written specifically for specialists, being virtually impenetrable to the uninitiated reader.

In the summer of 1996, rains flooded the Amazon, rendering it virtually impenetrable.

More sophisticated security devices on the windows, he added, "will make them virtually impenetrable."

Most of the area was wilderness, heavily forested and virtually impenetrable.

Its virtually impenetrable mineral exterior shields him against both physical and energy assaults.

Dense communities of these plants occur in the wild, to the extent that their density can make them virtually impenetrable.

The darkness was so dense as to be virtually impenetrable.

It's not hard to understand why the fortress proved virtually impenetrable.

Brazil's defense has spun a web that has been virtually impenetrable.