for liquefied gas carriage are built with a double hull throughout the cargo length. The insulation system includes the following:

1. Primary Barrier: A thin membrane made of INVAR (36% Nickel, 64% Iron) with a thickness of 0.5 to 1.2 mm, forming the primary containment layer for the liquefied gas.
2. Primary Insulation box: A 200 mm thick layer of granulated Perlite insulation packed in plywood boxes, surrounding the primary barrier. Perlite is siliconised to make it impervious to moisture.
3. Secondary Barrier: A secondary membrane made of the same INVAR material is installed to prevent cargo leakage in case of primary barrier failure.
4. Secondary Insulation box: Another 200 mm thick layer of granulated Perlite is placed above the secondary barrier to provide additional insulation and prevent thermal transfer.

Invar (36% Ni, 64% Fe) is used for both the primary and secondary barriers. The reason for this choice is its exceptionally low coefficient of thermal expansion. This eliminates the need for expansion joints or corrugations in the membrane design. In addition, Invar remains strong and does not become brittle at the very low temperatures experienced by the liquefied gas. The thin and lightweight nature of Invar maximizes the cargo-carrying capacity of the tank.