"The first part of this project, are general about sandwich structures. A sandwich construction, consist of two plate outsides (facings) glued to a core in the middle. Sandwiches are used in construction that must have a low weight, but a high stiffness. This indicated racing cars, aeroplane, ship shelters. To understand a sandwich construction, the basis, is to understand the sandwich beam. The are given a short description to find the deflection of the beam. The rest of this project, regards the calculation of a homogeneous, isotropic sandwich shelters. The objective is to reduce the mass of 20ft sandwich shelters from TAM AS. The background for this project, was the article: “Optimal Stiffness Design Plates with Variable Core Densities”. When we use, the methods described in this article, we find the inverse stiffness of the shelters, and from this optimal facings thickness, shear modulus for the core material and d, to reduce the weight of the shelters. The optimization are do it graphically. In the optimized of the shelters, only the walls are optimized, because the roof and floor is not symmetrical. When we optimize the parameters, the weight of the shelters can be reduce with 43.2kg. This are approximately 7.3%. To verify the calculation of the inverse stiffness of the shelters, the deflection of the shelters was calculated both analytical and numerical with four random pressures. The largest difference between the analytical and numerical value was only8.8%, which is good."