They said impermeable, not impervious. There are lots of coatings and materials that are impermeable to liquids and gases. For starters, they did not say it w

They said impermeable, not impervious. There are lots of coatings and materials that are impermeable to liquids and gases. For starters, they did not say it was inert (like say, PFTE, which is super low energy), so just because it's impermeable doesn't mean it won't get attacked by gases or solvents. Most polymers are.