League of Legends Reforged Rune: Overheal

Converts 20−100% of the healing in excess of your maximum health into a shield for an amount of up to 10 (+9% of maximum health) (depending on level).

After 6 seconds, the shield decays by 2.5% of its maximum value each second. Receiving healing or dealing or taking damage will refresh the shield duration to 6 seconds.