PMI foam is available in both hard and soft forms.

1. The rigid foam is the crystalline or amorphous form of the foam at room temperature, and their glass transition temperature is higher than normal temperature. Therefore, the texture of the foam is hard at normal temperature.

2. The flexible foam, that is, the polymer constituting the foam has a melting point lower than normal temperature or the glass transition temperature of the amorphous polymer is lower than normal temperature, and the material is soft at room temperature.

3. Semi-rigid (or semi-soft) foam is a foam between the above two categories.

Foam plastics can also be classified into low foaming and high foaming. Generally, the expansion ratio (a multiple after the expansion is increased more than the volume before foaming) of less than 5 is called low foaming, and the ratio of more than 5 is called high foaming.

Foam plastic is a kind of polymer material formed by dispersing a large amount of gas micropores in solid plastic. It has the characteristics of light weight, heat insulation, sound absorption, shock absorption, etc., and its dielectric property is superior to matrix resin, and its application is wide. Almost all kinds of plastics can be made into foam, and foam molding has become an important field in plastic processing.

Foam is also called porous plastic. A resin made of resin as the main raw material with numerous micropores inside. Light weight, heat insulation, sound absorption, shockproof and corrosion resistant. There are soft and hard points. Widely used as insulation, sound insulation, packaging materials and car shells.

Compared with pure plastic, PMI foam has low density, light weight and high specific strength. Its strength increases with density, it has the ability to absorb impact load, has excellent cushioning and shock absorption performance, sound insulation and sound absorption performance, and thermal conductivity. Low rate, good thermal insulation performance, excellent electrical insulation performance, corrosion resistance and mold resistance. Flexible foam has excellent properties such as elasticity.