If the open cell structure accounts for 90% -95%, the foamed plastic body of epp product is called open cell foam, otherwise it is called closed cell foam. Generally, some plastics can be made into foam plastics in more than one way, so they can be made into open cell foam plastics or closed cell foam plastics.
　　If necessary, the foam with closed cell structure can also be made into an open cell structure by mechanical pressure or chemical method. Open cell foams of epp products have good sound absorption and cushioning properties, while closed cell foams have low thermal conductivity and water absorption.
　　According to hardness, foamed plastics can be divided into soft foamed plastics, semi hard foamed plastics and hard foamed plastics. When the elastic modulus of foam plastic is less than 70MPa at 23 ℃ and 50% relative humidity, it is called soft foam plastic; EPP products with elastic modulus greater than 700MPa are called rigid foam plastics; Foam plastics with elastic modulus between 70MPa and 700MPa are called semi-rigid foam plastics.
　　According to the density classification, foam plastics can be divided into low foaming, medium foaming and high foaming foam plastics according to different product densities. Low foaming foams are those with density greater than 0.4g/cm3 and gas solid foaming ratio less than 1.5; Medium foamed plastics are those with density between 0.1-0.4g/cm3 and gas solid foaming ratio between 1.5-9.0; High foaming foams are those with density less than 0.1g/cm3 and gas solid foaming ratio greater than 9.
　　Foaming method and basic principle: in the production of foam plastics, the principle of foam formation is different due to the different foaming methods and processes used for epp products. At present, most of the industrial production uses the molding of air foaming plastics. The following is a brief introduction to the foaming method of air foaming plastics and the formation principle of bubbles.