Due to different production processes and adjustable formulation components, polyurethane can be made into many different varieties of foam. There are several types of classification:

1. Hard bubble, soft bubble and semi-hard bubble
According to the soft and hard degree of polyurethane foam, it can be divided into soft polyurethane foam (referred to as polyurethane soft foam, PU soft foam), rigid polyurethane foam (polyurethane hard foam, PU hard foam) and semi-rigid polyurethane foam between the two (polyurethane semi-hard foam, foreign countries are also called semi-soft foam).

Polyurethane soft foam commonly known as polyurethane sponge, foam, this kind of foam plastic elasticity is good, mainly used in a variety of hot materials, buffer materials, such as vehicles and furniture sofa seats, cushions and armrests, mattresses, clothing padding and so on.

Polyurethane foam is harder in texture. Low density hard bubbles are mostly brittle materials. Most polyurethane rigid foam is closed cell structure, using low thermal conductivity foaming agent foaming, so low thermal conductivity, widely used in various thermal insulation fields. High density hard foam has good toughness and high strength.

Polyurethane semi-rigid foam has a certain open structure, its bearing performance is good, good vibration absorption performance, and is widely used in buffer materials, automotive parts and so on.

2. High density and low density foam
Polyurethane foam can be divided into high density and low density according to different uses.

3. Polyester polyurethane foam and polyether polyurethane foam
According to the type of oligomer polyol raw materials used. Polyurethane foam can be divided into polyether type and polyester type two.

Polyester polyurethane foam has high strength, but because the ester group is not resistant to hydrolysis, the hydrolysis resistance of the foam is poor, and the cost of polyester polyol is high, which also limits its application. The polyester type is often used in special applications such as clothing liners. The aromatic polyester polyurethane rigid foam has good toughness and is used for PIR structural plate. (Aromatic: A class of organic compounds whose molecules contain benzene rings are called aromatic compounds.)

Polyether polyols have rich varieties, relatively low cost and good hydrolysis resistance, so they are mainly polyether polyols in the soft bubble market, accounting for more than 90% of the market.

4.TDI (Toluene diisocyanate) type and MDI (diphenylmethane diisocyanate) type foam
According to the different types of polyisocyanate, polyurethane foam can be divided into TDI type, MDI type and TDI/MDI mixed type. At present, the polyisocyanate raw material of polyurethane hard foam has basically used crude MDI (also called PAPI), in the production of soft foam, these three types of isocyanate products exist, and some polyurethane foam is manufactured by liquefied MDI or prepolymer modified MDI.

Common massive soft bubbles are generally made of TDI, while those made of TDI are soft and have low density. The high resilience foam generally uses the mixture of TDI and PAPI (or modified MDI) as the isocyanate raw material, so as to obtain faster curing and load-bearing properties. In the past 20 years, full MDI molded soft foam with high resilience and fast aging and short production cycle has been developed, and has formed a certain market.

5. Polyurethane foam (PU foam) and polyisocyanurate foam (PIR foam)
According to the different isocyanate index, polyurethane rigid foam can be divided into polyurethane foam (PU foam) and polyisocyanurate foam (PIR foam).

The isocyanate index (which represents the content of NCO groups in the raw material) of the general polyurethane hard foam is about 100. When the isocyanate in the raw material is greatly excessive, the rigidity and flame retardancy of the prepared PIR foam are significantly higher than that of ordinary polyurethane rigid foam.

6. Open and closed cell foam
The pores in the closed cell foam are isolated from each other and float on the water surface. Most polyurethane rigid foam has a closed cell structure, which is because the shape of rigid foam is not very sensitive to temperature changes, and closed-cell foam with stable size can be prepared. The closed-cell polyurethane soft foam will change shape due to temperature, shrink and deform after cooling, and the size is unstable.

The pores in the open cell foam are interconnected and have no floating property in water. Most polyurethane soft foam has an open cell structure, and gas can pass through the foam body. Foam with a high porosity can be used for filtration and other purposes. Mesh foam is a soft or semi-soft foam with high porosity manufactured by a special process for filtering materials. There is also a kind of perforated polyurethane rigid foam, which can be used to make special vacuum foam insulation panels, etc., and the production is very small.