"Skillful Cree leatherworking lets you better protect your soldiers. All infantry and cavalry hitpoints increased."—In-game description
Cree Tanning is a technology in Age of Empires III that can be researched at a Trading Post built on a Cree settlement. Once researched, it increases the hit points of infantry, cavalry, and light infantry by 5%.
Cree Tanning is of questionable value due to the negligible hit points boost, but the bonus does stack with other hit point-boosting improvements, so it can sometimes be useful.