Air permeability refers to the ability of a rubber material to allow air or gases to pass through it. It is a critical property for applications where airtightness or controlled gas flow is required. The lower the air permeability, the better the rubber is at preventing gas leakage.

Factors Affecting Air Permeability in Rubber

1. Rubber Type:

   • Butyl Rubber (IIR) – Excellent air barrier properties, commonly used in inner tubes and seals.

   • EPDM (Ethylene Propylene Diene Monomer) – Moderate air permeability but good weather resistance.

   • Natural Rubber (NR) & SBR (Styrene-Butadiene Rubber) – Higher permeability, making them less ideal for airtight applications.

   • Fluoroelastomers (FKM, Viton®) – Low permeability with excellent chemical resistance.

2. Polymer Structure:

   • The molecular density and degree of crosslinking affect how easily gases pass through the material.

   • Polymers with tightly packed molecular chains, like butyl rubber, provide better resistance to air diffusion.

3. Thickness & Composition:

   • Thicker materials naturally reduce permeability.

   • Fillers and plasticizers can either enhance or degrade air-tightness, depending on their compatibility with the base polymer.

Applications Where Air Permeability Matters

• Tire Inner Liners – Butyl rubber is used to maintain air pressure.

• Seals & Gaskets – Prevents gas leaks in industrial applications.

• Medical Equipment – Used in inflatable devices and controlled gas flow systems.

• Gas Storage Bladders – Requires low permeability for efficiency.

For applications requiring airtightness, butyl rubber (IIR) and fluoroelastomers (FKM) are often the best choices.