Pykrete

Pykrete – a frozen composite material, originally made of approximately 14 percent sawdust or some other form of wood pulp (such as paper) and 86 percent ice by weight (6 to 1 by weight). During World War II, Geoffrey Pyke proposed it as a candidate material for a supersized aircraft carrier for the British Royal Navy. Pykrete features unusual properties, including a relatively slow melting rate due to its low thermal conductivity, as well as a vastly improved strength and toughness compared to ice. These physical properties can make the material comparable to concrete, as long as the material is kept frozen.

• MythBusters: What is Pykrete? – In the end, cost barriers and resource depletion had chilling effects on George Pyke’s icy fleets. For instance, it would’ve required more steel to house the frozen ice than it would’ve taken to build an entirely new ship. Also, by 1943, technology had caught up with necessity, with better equipped aircraft carriers in use.