an essential and distinguishing attribute of something or someone

the quality of being penetrable (by people or light or missiles etc.)

not admitting of penetration or passage into or through

Mysteriousness, complexity; the property of being puzzling or inexplicable.

The condition of being so tightly made that water cannot enter or escape.

The property of not allowing sound through.

The property of being being sealed in such a way that steam cannot leak out.

The property of being unaffected by or impervious to water.