###### Abstract  
Nowadays, fire-doors optimization is approached by using consolidated design guidelines and traditional materials, such as rock wool. Then, selected solution is directly tested in a mandatory fire-test. Unfortunately, few pieces of information could be retrieved either if the test succeeds or fails, which makes both improvements in the design and use of innovative materials difficult. Thus, in this work, a self-consistent finite element method (FEM) analysis is developed and assessed against experimental fire-test results, highlighting the critical parameters affecting the numerical simulations. Using this tool, a new fiberglass-containing foam, with improved acoustic and mechanical properties, as compared to the rock-wool, is studied as a potential insulating material for on-board fire-doors. The assessment of the performance of the new material demonstrates that, contrary to common believe, the effective thermal insulation capacity is not necessarily the critical factor in determining the fire-resistance of a fire-door. Using the validated FEM analysis, it has been proven that the reduction of the thermal bridges originated at the door edges allows, firstly, for the attainment of a fire-door 37% thinner and 61% lighter with respect to a traditional one, and, secondly, the use of new material as insulator in fire-doors that, even if less thermally capable, could improve other properties of the door, as an example its soundproofing. f 2020 10 5736 10.3390/app10175736 10.3390/app10175736 10.390/app10175736 10.  
door edges, the heat conduction through the door and the steel sheet thickness [2]. The thermal bridges influence both the temperatures on the unexposed side of the door and the distortions of the door as they create a high temperature gradient at the edges [2]. The steel sheets give structural strength to the door, but they convey heat by conduction, so the use of fire-resistant insulating materials is necessary in order to slow down the spread of heat and to comply with the regulations [1]. The market is now dominated by few categories of thermal insulators, such as mineral wool and extruded and expanded polystyrene [3]. For fire-proofing rock wool is the most widely used insulator on board as it presents a hard to surmount mix of cheapness and mechanical/physical properties: it has low thermal conductivity, and it is lightweight and not flammable [4]. However, the release of fibers due to damage to the doors may present environmental and health concerns [5]. Furthermore, its soundproofing performance, which is an important property in passenger ships, is relatively poor [6; 7]. As a consequence, there is a strong research interest for substitute materials. Several studies investigated the thermal, acoustic and environmental performances of materials at current, scarcely used, or even in prototypal stages [3]. These unconventional products can be manufactured using natural sources, such as residues of agricultural production and processing industries. Other sources are represented by recycled products or industrial plant byproducts [3]. Following this drive towards the development and use of new materials, an innovative sustainable insulating material has been developed through a foaming process, starting from fiberglass waste and natural alginate-based gels [8]. This material is an open cell foam and shows improved soundproofing capabilities compared to rock wool, which, as stated above, makes them potentially of interest in shipbuilding. The mechanical and thermal characteristics of the foam have been analyzed in this work, including the incombustibility test in order to fully comply with the FTP Code [1]. The use of novel materials or innovative fire-door design in shipbuilding is often retarded or even precluded due to the necessity to ensure compliance with established mandatory requirements. Among these, the FTP Code compliance test is perhaps the most demanding and expensive test.