The quality of being breathable; how easily air can move through a material or space.
From 'breathable' (able to breathe through) plus '-ness' (Old English nys, forming abstract nouns). A more formal variant of breathability that emerged in the late 20th century.
The distinction between 'breathability' and 'breathableness' is subtle—'breathability' became the standard scientific term while 'breathableness' remained more poetic and less common, showing how technical language specializes!
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