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Permeability Converter

Convert permeability: kg/(Pa·s·m²), perm.

3 units
6 decimals

1 kg/(Pa·s·m²) = 17405682955.484966 Perm (23°C)

About the permeability converter

Convert vapor permeance between kg/(Pa·s·m²) (SI) and the perm units used in building science. Permeance measures how readily water vapor passes through a material under a pressure difference — critical for vapor-barrier specification and condensation control in walls and roofs.

Frequently asked questions

  • What is a perm?

    A perm is the imperial unit of vapor permeance: 1 perm ≈ 5.72 × 10⁻¹¹ kg/(Pa·s·m²). Buildings codes use perms to classify vapor retarders.

  • What is the difference between Perm (0°C) and Perm (23°C)?

    They use slightly different reference conditions for water vapor saturation, so their conversion factors differ by less than 0.5%.

  • Is high or low permeance better for a vapor barrier?

    Low. A Class I vapor retarder has ≤0.1 perm. Higher-permeance materials let more vapor through and are not vapor barriers.

More fluids converters

Flow → Flow — Mass → Flow — Molar → Mass Flux Density → Concentration — Molar → Concentration — Solution → Viscosity — Dynamic → Viscosity — Kinematic →

Complete list of permeability units