Minecraft wiki entry for Piston, associated text: It is invisible and non-solid in Java Edition, and cannot be broken without the use of commands or TNT. Although it is non-solid, fluids cannot pass through it. It also prevents players from building at its location. Mobs can see through it, but cannot walk through it. The game treats the block as a stone block when it comes to the player's footstep sounds. It is similar to Invisible Bedrock in properties with the exception that the player can walk through the moving piston but not invisible bedrock.