Shield is an effect keyword in Bloons Card Storm that adds an additional layer of health to Bloons and Heroes. Unlike health, there is no limit to the amount of Shield a Bloon or Hero can have. If a Bloon or Hero with a Shield takes damage, the Shield takes damage first. Bloons and Heroes with a Shield are surrounded by a transparent bubble. Shields are not affected by Armor.
Shields on Bloons increase their health, but do not add to the damage the Bloon deals to the opponent's Hero if it leaks. Shields do not trigger On Damaged keyword effects when taking damage unless the hit also damages the Bloon inside it (i.e., it deals more damage than the Bloon has Shield). Some Bloons, such as the Bolstered Bloon and Buddy Bloon, start with a certain amount of Shield when played. In the card text, this is written as "Shield <amount>".
Shields on Heroes block damage caused by Bloons. Heroes can gain Shields from certain cards and Hero Abilities. Wall Of Trees is unique in that it grants the Hero a Shield and has an effect that triggers the next time it is destroyed.