* Density: Lead is extremely dense. Even a small amount of lead will significantly increase the weight of the coffin.
* Buoyancy: For an object to float, it needs to displace an amount of water equal to its own weight. The lead lining makes the coffin significantly heavier than a standard wooden coffin, making it difficult to displace enough water to achieve buoyancy.
* Water Absorption: Wood absorbs water, which could add to the coffin's weight and further reduce its chances of floating.
While it's theoretically possible that a very small, lightweight coffin with a minimal amount of lead lining might float, in practical terms, a lead-lined coffin is designed to sink.