Permeability Converter

Kilogram/Pascal/Second/Square Meter (kg/Pa/s/m²)

The SI unit of permeability, representing the mass of gas that permeates through a material per unit area, time, and pressure gradient. 1 kg/Pa/s/m² = base SI unit. Used in thermodynamics and materials science for precise calculations.

Definition: Describes how readily a substance (gas, liquid, or vapor) passes through a material under pressure difference.

Permeability at 0°C

Material permeability measured at 0°C (freezing point). 1 perm @ 0°C ≈ 5.72 × 10⁻¹¹ kg/Pa/s/m². Used for low-temperature applications and refrigeration systems.

Application: Cold storage, cryogenic systems, and materials testing at low temperatures where permeability changes significantly.

Permeability at 23°C

Material permeability measured at 23°C (room temperature). 1 perm @ 23°C ≈ 5.75 × 10⁻¹¹ kg/Pa/s/m². Standard reference condition for most building and material applications.

Most common use: Building materials, packaging films, membranes, and general materials testing. 23°C is standard laboratory temperature.

Permeability (inches)

North American unit of permeability using inches as the length dimension. Both 0°C and 23°C versions exist for low and room temperature applications. Used in US building codes and material specifications.

Application: American HVAC systems, building membranes, moisture barriers, and North American construction standards.

Understanding Material Permeability

Permeability describes a material's ability to allow substances to pass through it. Key concepts:

• Driven by concentration or pressure gradient: Substance moves from high to low concentration/pressure
• Relates to diffusion: Governed by Fick's laws of diffusion through materials
• Different for different gases: Smaller molecules (O₂, N₂) permeate faster than larger ones (CO₂, water vapor)
• Material-dependent: Polymers vary widely; metals are extremely low permeability
• Critical for applications: Packaging (shelf life), building envelopes (moisture control), medical devices (oxygen transmission)

Temperature Dependence - CRITICAL

Permeability increases significantly with temperature (roughly exponential):

• Typical polymers: Permeability doubles every 10-15°C increase
• Water vapor through materials: Can increase 5-10× from freezing to room temperature
• Oxygen through plastics: Increases 2-4× over typical service range
• Gas diffusion through membranes: Follows Arrhenius relationship

Always specify measurement temperature! Permeability values at different temperatures can differ by orders of magnitude, making temperature essential information.

Gas-Specific Permeability Variations

Different gases have very different permeabilities through the same material:

• Oxygen (O₂): Moderate permeability; critical for food packaging shelf life
• Nitrogen (N₂): Lower permeability than oxygen (important for gas barrier)
• Water vapor (H₂O): Often much higher permeability than gases; critical for moisture barriers
• Carbon dioxide (CO₂): Often higher permeability; affects carbonated beverage shelf life
• Helium (He): Very high permeability; used to test membrane integrity

This is why packaging materials must be specified for specific applications (O₂ barrier vs moisture barrier).

Typical Permeability Values (Gas Permeability Examples)

• Polyethylene (PE), O₂ @ 23°C: ~200-500 cm³·μm/(m²·day·atm)
• Polypropylene (PP), O₂ @ 23°C: ~50-100 cm³·μm/(m²·day·atm)
• PET (polyester), O₂ @ 23°C: ~5-10 cm³·μm/(m²·day·atm)
• Aluminum foil: Essentially zero (excellent barrier)
• Glass: Essentially zero (perfect barrier)
• Paper, water vapor @ 23°C: ~100-200 g/(m²·day) depending on type
• Polyimide film, O₂: ~1-5 cm³·μm/(m²·day·atm) (excellent barrier)
• Natural rubber, O₂: Very high permeability (poor barrier)
• SiO₂ coating: Can reduce permeability 1,000× or more
• Brick (porous): High water vapor permeability (breathable)

Critical Applications of Permeability

• Food & beverage packaging: Oxygen and moisture barriers determine shelf life
• Building envelopes: Vapor barriers control moisture to prevent damage and mold
• Medical devices: Oxygen transmission through materials for wound dressings, contact lenses
• Flexible films & bags: Material selection based on oxygen permeability for product protection
• Electronics & batteries: Moisture permeability affects reliability and lifespan
• Membranes & separation: Selective permeability for gas separation, dialysis
• Coatings & paints: Prevent moisture penetration in protective coatings
• Composite materials: Permeability of resin matrix affects service environment resistance

Key Conversion Factors

• Permeability @ 23°C ≈ Permeability @ 0°C × (slight difference)
• Permeability inches slightly differs from metric due to length unit
• Temperature effects dominate: 10°C change can double or halve permeability
• Gas-specific: Oxygen permeability ≠ water vapor permeability for same material
• 1 SI unit = 1.745 × 10¹⁰ perm @ 23°C (approximately)
• Barrier coatings can reduce permeability by 1,000-10,000× or more
• Activation energy for permeation: Typically 20-40 kJ/mol for polymers