Abstract: An insulation system for marine tanker or land based liquid natural gas containers is formed in prefabricated modules bolted to an inner wall of the container. Adjacent modules are connected to provide a continuous insulation, liquid barrier and tension membrane. The confined liquid is in contact with a layer of closed cell polyurethane foam that incorporates means for relieving thermal stresses. The liquid tight primary foam layer is backed by a liquid tight fiberglass tension membrane and an additional layer of polyurethane foam. The fiberglass membrane is connected to cruciform fittings in the tank corners for reaction of contraction induced tensile forces. Handling and installation of the system is simplified by prefabricating the several layers of insulation and fiberglass membrane with a plywood panel supporting the system and providing an interface with the inner hull of the ship or inner tank surface. Damage and leak detection sensors are incorporated in the module at the membrane.