Chlorofluorocarbons (CFCs) were widely used as blowing agents for foams and packing materials due to their stability and non-toxicity. They help create bubbles or cavities in the foams, giving them their lightweight and insulating properties.

B. tyre industry: CFCs were not used as blowing agents in the tyre industry; they were primarily associated with foam production and other applications.

C. refrigerant: While CFCs (like Freon) were widely used as refrigerants, the question specifically asks about their application as a blowing agent.

D. propellant: CFCs were also used as propellants in aerosol sprays, but the primary application for a blowing agent is in the foam industry.

The correct answer is option A - foam industry.