The interconnected micropores are called open-cell foams, and the closed ones are called closed-cell foams. There are two kinds of foam plastic, rigid and soft. According to the standards of the American Society for Testing and Materials, at a temperature of 18 ~ 29 ℃, within a time of 5s, around a round rod with a diameter of 2.5cm for one week, if it does not break, the test sample is a flexible foam; otherwise it is a rigid foam . Foam plastic can also be divided into two types of low foaming and high foaming. Generally speaking, the expansion ratio (a multiple of volume increase after foaming before foaming) of less than 5 is called low foaming, and greater than 5 is called high foaming.
1. Rigid foam plastics: At room temperature, the polymers that make up foam plastics are crystalline or amorphous, and their glass transition temperature is higher than normal temperature. Therefore, the texture of foam plastics is hard at normal temperature.
Second, the flexible foam plastic, that is, the polymer constituting the foam plastic, has a melting point lower than normal temperature or an amorphous polymer whose glass transition temperature is lower than normal temperature, and the material has a soft texture at normal temperature.
3. Semi-rigid (or semi-soft) foam is a foam between the above two categories.