Cavity walls consist of two faces with an empty space in between to apply thermal insulation boards or panels. This building technique is widely used across Italy because it ensures a high degree of thermal comfort by keeping the interior walls warm. Walls are usually either curtain walls or load-bearing walls: in the latter case, the outer face often has an at-sight masonry finish (bricks) and protects the load-bearing wall against bad weather while preserving the inner thermal insulation, as the latter is no longer accessible. The advantage of double walls is that the load-bearing wall on the insideaccumulates and preserves heat at length. Wall performance is further improved by creating ventilated air spaces, namely an air barrier between the outer face and inner face on which the insulation boards are applied: air circulation maintains a low concentration of water vapor and provides a further degree of protection for the insulation over time. Air circulation is ensured by means of vents in the outer face and the use of spacers between the outer face and the insulation layer. In this type of application, we recommend using a product that can guarantee constant and durable performance over a long period of time, since the insulation layer cannot be accessed during a building's entire life cycle, and that affords a high resistance to water absorption. Extruded polystyrene has all these properties and, since it is also breathable, there is no need for laying a vapor barrier or air barrier; X-FOAM^® LMF is especially easy-to-use and it makes laying fast thanks to the length of the boards (2800 mm) because they cover the entire wall from top to bottom. In case of buildings with a load-bearing structure and outer curtain walls, thermal bridging can be easily solved by passing the thermal insulating layer outside the pillars.