1) Imperviable 2) Impervious 
[adj] - resistant to penetration by grease or oil or wax
Papers which have a high resistance to penetration by grease or fats found in various foodstuffs. The paper is produced by prolonged beating in the pulp stage, providing an end product which is close and to a degree transparent. Sizing adds the greaseproof characteristic. Widely used for wrapping foods.
adjective resistant to penetration by grease or oil or wax; `greaseproof wrapping paper`