Cobweb
Cobweb is a block that slows down movement and can be obtained using shears or a Silk Touch-enchanted sword in Java Edition. When broken with a regular sword, it drops string. Water, pistons, or lava can also destroy cobwebs, but they drop nothing.
Cobwebs generate naturally in mineshafts, stronghold libraries, abandoned villages, igloo basements, woodland mansions, and trial chambers. They can also form when an entity with the Weaving effect dies.
Players and most mobs move at 25% of normal speed in cobwebs, with gravity-affected entities falling slowly through them. Cobwebs prevent fall damage and can be used as a delaying mechanism in redstone circuits. Arrows pass through them without slowing down.
Cobwebs can be brewed into Mundane Potions or used to craft a Potion of Weaving. When placed on blue ice with additional slowing effects, cobwebs create one of the slowest movement conditions possible in Minecraft.