Polyurethane foam blowing agents are specialized substances that act as "gas generators" during the production of polyurethane (PU) foam. Their core function is to create a large volume of gas within the liquid polyurethane mixture. Blowing agents are one of the important additives in polyurethane foam formulations. They are divided into chemical blowing agents and physical blowing agents (auxiliary blowing agents). In polyurethane foams, the chemical blowing agent is typically water. Other substances that vaporize by absorbing heat to expand the foam material are classified as physical blowing agents.

The carbon dioxide gas generated by the reaction between water and isocyanate causes the foam mixture to expand, foam, rapidly increase in viscosity, and cure. In traditional polyurethane foams, water is primarily used as a blowing agent for flexible foams, as well as in microcellular elastomers, semi-rigid foams, and rigid foams.

The polyurethane foam with water blowing agent only without physical blowing agents is generally for non-thermal insulation application, include high-density structural foam (Wood imitation), packaging materials, filling materials, etc., or for situations with low thermal insulation requirements.

Due to the relatively high thermal conductivity and strong permeability of carbon dioxide, water is rarely used in rigid polyurethane foam that require high thermal insulation performance. The production of polyurethane rigid foam for insulation generally need to use physical blowing agents. This is because, during the initial mixing of materials in rigid foam production, a significant amount of heat is generated within ten seconds. The blowing agent is needed to absorb part of this heat. In the production of polyurethane flexible foam, to achieve low-density soft foam without causing stiffness due to excessive water usage, it is generally necessary to control the amount of water and add an appropriate amount of physical blowing agent as an auxiliary foaming agent.

Below is an introduction to several common blowing agents:

1. HCFC-141b
   Name: 1,1-dichloro-1-fluoroethane; dichlorofluoroethane.
   HCFC-141b was once a widely used and high-performance physical blowing agent in the field of polyurethane rigid foam. However, due to its environmental issues, now it has been restricted and phased out globally, making it a "transitional" product. Its performance is very close to the banned CFC-11 (Freon). It has a moderate boiling point, high foaming efficiency, good compatibility with two raw materials materials—polyol and isocyanate, and produces foam with excellent thermal insulation properties. It was mainly used in the insulation of refrigerators/freezers, construction insulation panels, spray foam for pipes, and refrigerated containers. By 2015, the disabling of it has been completed in refrigerators and freezers. By 2026, a comprehensive phase-out for all polyurethane foam industries will be finished.
2. Cyclopentane
   Name: cyclopentane. Its molecular formula is C₅H₁₀, with a molecular weight of 70.1. The CAS number is 287-92-3.  It has zero ODP and a low GWP, making it an environmentally friendly blowing agent. It offers high foaming efficiency, and the foam exhibits excellent thermal insulation performance. Its cost is relatively competitive among eco-friendly blowing agents. It is specifically used for rigid foam that requires extremely high thermal insulation performance, such as household appliances/refrigerators/freezers/ and water heaters/construction insulation/ metal sandwich panels/cold storage panels/ In industrial insulation/ pipes/storage tanks, etc.

3. Pentane
   Pentane blowing agents are a commonly used type of environmentally friendly physical blowing agent, including N-Pentane and I-Pentane, has zero ODP and very low GWP, making them eco-friendly hydrocarbon blowing agents. They are representative hydrocarbon blowing agents in rigid foam (especially for building insulation panels and pipe insulation), they are mainly used in building Insulation: EPS/XPS sandwich panels/ continuous panels/spraying Industrial Insulation/I pipes/ storage tanks/some Appliances/ water heaters/solar water tanks where the thermal insulation performance requirement is slightly lower.
4. Liquid carbon dioxide
   Carbon dioxide as a blowing agent is an environmentally friendly new technology. It mainly exists in two forms: one is directly used as a physical blowing agent, the other acts as a chemical blowing agent, releasing CO₂ gas through chemical reactions. It has a wide range of applications and minimal environmental impact with zero ODP and lower GWP. In the polyurethane industry, it is used for low-density block flexible foam, where it is mixed into the polyurethane reaction mixture via specialized equipment under appropriately reduced pressure to function as a blowing agent. In specific processes, liquid carbon dioxide also can be used as a blowing agent for polyurethane rigid foam.
   
   
5. Methylene Chloride
   Dichloromethane (Methylene Chloride, shortened to MC, molecular formula: CH₂Cl₂) is primarily used as an "auxiliary physical blowing agent"in the polyurethane industry. It is an excellent low-boiling-point organic solvent and can serve as an auxiliary blowing agent for flexible polyurethane foam and used as a cleaning solvent for foaming equipment. It is also used as an extractant for cellulose acetate film, pharmaceuticals, fragrances, and oils, fire extinguisher.