Marine composites, especially those used in ship structures, are mainly polymer - based composites. They can be classified into two main types according to structure: laminates (fiber - reinforced composites) and sandwich structure composites. The most significant advantage of the marine composite sandwich structure lies in its “lightweight structure”, which helps reduce fuel consumption. Marine composites are mainly required to be lightweight yet strong, capable of effectively increasing the reserve buoyancy of the ship. They should have integrated structural functions, having other properties such as noise reduction, vibration absorption, and heat insulation while meeting the structural load requirements. They need to be corrosion - resistant to meet the harsh marine environment requirements of high salt, high humidity, and ultraviolet radiation, and be resistant to aging to meet the long - life requirements of ships.

PMI foam is lightweight, strong, heat - insulating, sound - insulating, corrosion - resistant, and aging - resistant, fully meeting the requirements of marine composites. It is commonly used as a sandwich in structures such as decks and bulkheads. After long - term verification, PMI foam has become the preferred material for ship heat - insulation and sound - insulation.