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 11% of your maximum health (depending on level).

After 6 seconds, the shield decays by 1% of its maximum value every 0.25 seconds. Receiving healing, dealing damage, or taking damage will refresh the shield duration to 6 seconds.