Air Permeability Testing and Its Effect on Comfort

Air permeability predicts wind resistance and breathability, making it one of the most useful numbers in technical textile selection.

This guide explains the underlying principle, the numbers that matter and the checks that keep results consistent.

Measurement method

Air is drawn through a defined area at a fixed pressure differential, and the flow rate is reported per unit area.

For most programmes the decision is taken during development, when changing the specification still costs nothing more than one sampling round.

Values span from below one litre per square metre per second for windproof shells to hundreds for open meshes.

Where a standard exists, name the standard number, since a value without a method cannot be verified by a third party.

Low permeability blocks wind but raises condensation risk during sustained effort, which is why balance is activity dependent.

Train operators on what the parameter looks like when it is wrong, since most defects are visible long before testing.

Calendering, coatings and laminates reduce permeability sharply, so retest after finishing rather than assuming.

Repeat the test when the fabric, the mill or the finishing route changes, as previous results no longer apply.

Combine with thermal resistance and moisture vapour transmission to characterise a fabric fully.

Ask for the cost of the requirement to be shown separately, so it can be weighed against the benefit it delivers.

Handled early, the requirement costs little and protects the launch date; handled late, it becomes an argument about responsibility.