Pykrete (also known as picolite) is a composite material made of approximately 14% sawdust (or, less frequently, wood pulp) and 86% water by weight then frozen, invented by Max Perutz and proposed during World War II by Geoffrey Pyke to the Royal Navy of the United Kingdom as a candidate material for making a huge, unsinkable aircraft carrier, Project Habakkuk, actually more of a floating island than a ship in the traditional sense. Pykrete has some interesting properties, notably its relatively slow melting rate (due to low thermal conductivity), and its vastly improved strength and toughness over pure ice, actually closer to concrete, while still being able to float on water. Pykrete is slightly harder to form than concrete, as it expands while freezing, but can be repaired and maintained from the sea's most abundant raw material.


Pyke managed to convince Lord Mountbatten of the worth of his project some time around 1942, and trials were made in two locations in Alberta. Blocks of Pykrete were attacked with various explosives and it was found that a charge corresponding to a torpedo warhead would have made only a minor dent in the planned Habbakuk carrier.

At the Quebec Conference of 1943 Mountbatten brought a block of Pykrete along to demonstrate its potential to the bevy of admirals and generals who had come along with Winston Churchill and Franklin D. Roosevelt. Mountbatten entered the project meeting with two blocks and placed them on the ground. One was a normal ice block and the other was Pykrete. He then drew his service pistol and shot at the first block. It shattered and splintered. Next, he fired at the Pykrete to give an idea of the resistance of that kind of ice to projectiles. The bullet ricochetted off the block, grazing the trouser leg of Admiral Ernest King and ending up in the wall. The Admiral was impressed by Mountbatten's unorthodox demonstration. Thus, the small pilot project was given the go-ahead, but the main Project Habbakuk was never put into action. The funds simply were not available due to other WWII projects, as well as the belief that the tides of the war were beginning to turn in favour of the Allies using more conventional methods. (This explanation for demise of Project Habbakuk was confirmed by Max Perutz in 1947 in a private conversation with Oliver French.)

According to the memoirs of British General Ismay:

"A good deal of consideration, much of it highly technical, was also given to the feasibility of building floating platforms which could either be used by fighters to support opposed landings until such time as airfields ashore were available, or act as staging points for ferrying aircraft over long distances. The idea as originally conceived by a member of Combined Operations staff, and vehemently supported by Mountbatten, was that these floating platforms should be constructed out of icebergs. They would be provided with engines which would enable them to steam at slow speed, and with refrigeration plants to prevent them melting. They would be unsinkable. The whole thing seemed completely fantastic, but the idea was not abandoned without a great deal of investigation. Various alternative methods of construction were then considered by the United States naval authorities, but in the end there was general agreement that carriers and auxiliary carriers would serve the same purpose more effectively."

Since WWII pykrete has remained a scientific curiosity, unexploited by research or construction of any significance. New concepts for pykrete however crop up occasionally among architects, engineers and futurists, usually regarding its potential for mammoth offshore construction or its improvement by applying super-strong materials such as synthetic composites or Kevlar.


Pykrete has a crush resistance of greater than 21 megapascals (3,000 psi) so a 25 mm (1 in) column could support the weight of a typical car. The wood pulp also makes the pykrete stable at higher temperatures. If a .303 caliber bullet is fired at the pykrete, it will penetrate only 16 cm (6.5 in).


Pykrete can be easily formed using water and any porous and fibrous material, such as shredded paper or sawdust. Anything that can be molded with this wet pulp can be frozen into a strong and non-brittle solid.

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