Barrier walls are designed to allow water to be absorbed but not penetrate the wall, and include concrete and some masonry walls.

At this point, electron microscopy can no longer penetrate the wall.

The pointed ends of ookinete penetrate the wall of stomach and comes to lie below its outer epithelial layer.

Or, lacking the energy to penetrate a wall, it would bounce back (reflection) or in the extreme case, bury itself inside the wall (absorption).

Water penetrates walls and can do serious external and internal damage.