Stoppered
Stoppered is a potion effect that blocks effects from splash potions and tipped arrows.
Brewing
A Potion of Warding can be brewed from an Awkward Potion using a Milk Bottle.
Effects
Splash potions, lingering potions, and tipped arrows do not apply their effects to a player with Stoppered. This includes Splash Bottles of Milk. The player will still gain effects when drinking a potion (including Milk, which will clear Stoppered and all other effects as usual). Effects that are applied in other ways, such as the Poison from a Cave Spider hit, will still affect a player with Stoppered.
Beacons
A level 4 Beacon can be configured to grant the Stoppered effect.