- Sofa bed City. Mechanism of transformation-Eurobook. In the sofa a large box for linen. Block of 672 independent springs !! A layer of polyurethane foam and Spunbond is laid above the springs. It provides elasticity and softness. The sofa perimeter is reinforced with high-strength polyurethane foam. This protects the sofa from subsidence. The sofa is designed for everyday use.