The word 'impermeable' is an adjective, a word used to describe a noun. An adjective does not have a plural form.
The noun form of the adjective 'impermeable' is impermeability.
The noun 'impermeability' does not have a plural form.
The plural form of plastic is plastics.
The plural form of building is buildings.
The plural form for the noun 'material' is materials.
The plural form is technologies.
The plural form of apparatus is apparatuses. It has no foreign plural.
impermeable
There is no plural form. Do and Do not are verbs
The plural form of him, her, or it is them. (objective pronouns)
Bridges is the plural form of bridge.
The plural form of "is" is "are."
The plural form of "I" is "we."
The plural form of "was" is "were."
The plural form of mouth is mouths. The plural form of month is months. The Mounth is a range of hills in Scotland and does not have a plural form.
"Groceries" is the plural form of "grocery."
"Beliefs" does not have a plural form, as it is already plural. Beliefs is the plural form of belief.
The plural form of the demonstrative pronoun 'that' is those.
The plural form is metres.