"Nootka bark cloth increases villager hitpoints."—In-game description
Note that Fishing Boats are affected by Nootka Bark Clothing since they are classified as villagers.
Nootka Bark Clothing benefits any civilization greatly in making their villagers harder to kill. However, civilizations who already have high villagers with high hit points, especially the French with their Coureur des Bois and the Germans with their Settler Wagon, will see a dramatic effect.