Used when talking about something that stops movement, like walls or dense areas. The old castle's walls were once penetrable, but now they're reinforced.
Pro Tip 2/3
Ease of Entry
Describes how simple it is to enter or go through something physical. The once impassable cave is now easily penetrable by tourists.
Pro Tip 3/3
Literal Meaning
Focuses on the actual, literal ability to pass through an object or substance. This fabric is penetrable by water, so it's not good for raincoats.