Lava sponges

Lava sponges soak up lava. When soaked they become hot.

Tiers

Sponge	Reach	Search limit	Turns into
Lava Sponge	6 blocks	65	Hot Lava Sponge
Compressed Lava Sponge 1x	10 blocks	512	Hot Compressed Lava Sponge 1x
Compressed Lava Sponge 2x	16 blocks	4,096	Hot Compressed Lava Sponge 2x
Compressed Lava Sponge 3x	22 blocks	32,768	Hot Compressed Lava Sponge 3x
Compressed Lava Sponge 4x	28 blocks	262,144	Hot Compressed Lava Sponge 4x
Compressed Lava Sponge 5x	34 blocks	2,097,152	Hot Compressed Lava Sponge 5x

Getting them

Shaped ➜ Lava Sponge

Lava Sponges are also found in bastion remnants and Nether fortresses, and the Ender Dragon drops Compressed Lava Sponge 2x (Loot). The Lava Sponge Trader in the Nether sells every tier.

Hot sponges

WARNING

Hot lava sponges burn anything that walks on them, like a magma block. Sneak to cross them safely.

A hot lava sponge cools the moment it is placed in a snowy biome, the same biomes where snow foxes spawn (for example Snowy Plains, Snowy Taiga, Grove and Frozen Peaks). It turns back into the lava sponge of the same tier.

Outside of snowy biomes, cool it in a Freezer:

Freezer ➜ 10 sLava Sponge

Freezer ➜ 10 sCompressed Lava Sponge 5x

A normal furnace does not work on hot sponges.