How to Choose Physical Blowing Agents for Producing Low-Density Flexible PU Foam?

In the production of lightweight, high-resilience flexible PU foam, physical blowing agents are indispensable. They generate gas through physical changes, forming a uniform cell structure in the PU reaction system and significantly reducing density.

Main Types and Characteristics of Physical Blowing Agents

* GWP values are based on the IPCC Sixth Assessment Report.
* *For supercritical CO₂, “boiling point” refers to its sublimation temperature at atmospheric pressure; critical temperature is 31.1°C.

Detailed Analysis: How to Choose Your Blowing Agent

Low-Boiling Hydrocarbons – Economical and Eco-Friendly Choice
These agents are cost-effective and widely used for producing medium–low density foam. Production requires explosion-proof equipment, strict safety measures, flame retardants, and cell-opening agents for stable structure.

Supercritical CO₂ – Technology-Driven Innovation
CO₂ is currently the most eco-friendly blowing agent. Under specific temperature and pressure (about 31°C and 7.4 atm), it becomes supercritical and expands rapidly upon injection, producing ultra-low-density nano-cell foam. This requires advanced equipment but represents the industry's future direction.

Water – Cost-Effective Choice
Water foaming is low-cost and fully eco-friendly. It reacts chemically with raw materials to generate gas. To avoid excessive hardness, precise formula adjustment and specific catalysts are needed to balance foaming speed and curing.

Blended Blowing Agent Technology – Optimizing Performance and Cost

Cyclopentane / HFC-245fa (7:3): Combines cyclopentane’s low cost with HFCs’ ability to improve cell structure and reduce shrinkage, ideal for 15–20 kg/m³ packaging foam.

Water / Supercritical CO₂: Common in automotive seat foam (18–22 kg/m³), where water controls initial foaming and CO₂ refines cell size, reducing urea bonds and improving softness while achieving target density.

Key Considerations When Selecting a Blowing Agent

Product Density: For ultra-low density, HFCs or supercritical CO₂ are recommended; for medium–low density, cyclopentane or water is practical.

 Process Conditions: Assess whether your equipment supports high-pressure or explosion-proof requirements.

 Cost Budget: Water is cheapest, followed by cyclopentane; HFCs are more expensive.

 Safety & Regulations: Blowing agents must comply with environmental and safety standards, with proper safety measures in production.

Future Trends – Emerging Eco-Friendly Blowing Agents

Hydrofluoroolefins (HFOs): Extremely low GWP, replacing HFCs, though currently more costly.

Liquid CO₂: Injected at low temperatures to avoid high-pressure equipment, offering new solutions for small–medium scale production.

Choosing the right physical blowing agent involves balancing target density, process capabilities, environmental compliance, and cost. Cyclopentane and water are common, economical options, while HFCs and supercritical CO₂ suit high-performance or ultra-low-density applications. The industry is shifting toward greener solutions, driving innovation in PU foaming technology.