Understanding permeability units here
This page focuses on mass-based permeability expressed in kilograms per pascal second square meter. That framing shows up when you relate pressure-driven flow through a barrier with a clear kg/s story. You will also spot a few legacy rows lifted straight from older unit tables (including “permeability at 0 °C” style labels). Those entries are fixed conversion constants to the SI row: they rename the number you already have; they do not fetch live gas properties or run a simulation for you.
How permeability conversion works on this sheet
Pick the row whose label matches the stamp on your PDF. Multiply by the factor that takes that row to kg/(Pa·s·m²), then divide by the factor for the row your customer wants printed. Temperature words in the legacy labels describe where those constants came from on the reference table, not a slider you adjust inside this widget.
Result = Value × (source as kg/(Pa·s·m²) per unit) ÷ (target as kg/(Pa·s·m²) per unit)
If your discipline talks Darcy or prefers volumetric permeability with different conventions, translate through whatever bridge your standards body publishes. This screen stays faithful to the factors baked into our unit list so spreadsheet comparisons stay dull and dependable.
What each row is trying to say
Sparse menu by design: you should not need a philosophy degree to pick a line item.
kg/(Pa·s·m²)
Factor: 1 (base)
Straight SI transport coefficient when mass flow scales with pressure drop across the rated area.
Permeability (0 °C)
Factor: legacy table constant
Matches the frozen-in number from historical references. Good for parity checks, not for sneaking temperature logic past a peer review.
Permeability (23 °C)
Factor: alternate legacy constant
Same story with a different reference temperature baked into the old listing. Compare against 0 °C only after you understand what your document actually measured.
Permeability inches (0 °C)
Factor: inch-scaled legacy entry
Inch language for teams still thinking in membrane sheet thickness quirks. Conversion to the SI row is deterministic, interpretation in your membrane model is still your job.
Permeability inches (23 °C)
Factor: warm-leaning legacy entry
Parallel to the 0 °C inch row with the other tabulated constant. Useful when you mirror a competitor chart line for line.
Quick reference table
The numeric spread is enormous, so this is a guide to relationships, not something to memorize on a coffee lid.
| From | To | Note | Tip |
|---|---|---|---|
| Legacy “permeability” | kg/(Pa·s·m²) | fixed factor | Use dropdown exact label |
| Permeability (0 °C) | Permeability (23 °C) | ratio of tab factors | Parity check only |
| Permeability inches (0 °C) | kg/(Pa·s·m²) | inch-era constant | Mind label spelling |
| Permeability inches (23 °C) | kg/(Pa·s·m²) | warm listing | Compare to SI base |
| kg/(Pa·s·m²) | Same (sanity) | factor 1 | Baseline for audits |
| Outside tab (Darcy) | This page | needs bridge law | Use your standard first |
Keeping expectations friendly
Membranes, soils, and packaging films all wear the word “permeability” like a crowded hat. Match the definition section of your test standard (mass versus volume, which partial pressure, which thickness) before you celebrate two spreadsheets that finally agree.
When in doubt, carry uncertainty bounds from the lab chart. Converting digits precisely does not squeeze extra physics out of a thin datasheet footnote.
Permeability FAQ
Does the temperature in the label auto-adjust?
No. It tells you which legacy constant you picked. Real temperature dependence still lives in your material model.
Why include inch rows?
Because suppliers still ship charts that way. Converting faithfully beats arguing with a faxed curve from 1998.
Can I compare to Darcy results directly?
Only after you convert through the definition your reference uses for porous media. The factor path differs from thin-film mass permeation paths.
What pairs with pressure in a back-of-envelope?
Pressure drop in pascals, area in square meters, and consistent mass units on the flow side. When one leg drifts into psi or odd areas, pause and realign before you multiply.