Pykrete

Pykrete is a frozen composite material 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 huge, unsinkable aircraft carrier for the British Royal Navy. Pykrete has some interesting properties including its relatively slow melting rate (because of low thermal conductivity) and its vastly improved strength and toughness over ice; it is closer in form to concrete.

Pykrete is slightly more difficult to form than concrete, as it expands during the freezing process. However, it can be repaired and maintained using seawater. The mixture can be moulded into any shape and frozen, and it will be extremely tough and durable, as long as it is kept at or below freezing.

Geoffrey Pyke managed to convince Lord Mountbatten of the worth of his project (actually prior to the invention of pykrete) some time around 1942, and trials were made at two locations in Alberta, Canada. The idea for a ship made of ice impressed the United States and Canada enough that a 60-foot (18 m)-long, 1,000-ton ship was built in one month on Patricia Lake in the Canadian Rockies. It was, however, constructed using plain ice (from the lake), before pykrete was considered. It took slightly more than an entire summer to melt.

Plain ice proved to be insufficiently strong. Pyke learned from a report by Herman Mark and his assistant that ice made from water mixed with wood fibres formed a strong solid mass—much stronger than pure water ice. Max Perutz later recalled:

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