For many years, performance testing of water-based (industrial) paint systems for exterior applications has focused on liquid water permeability and durability. This is reflected in EN 927-2 Paints and varnishes - Coating materials and coating systems for exterior wood - Part 2: Performance specification (2022), where test methods for both characteristics are indicated as mandatory tests. For 30 years now we have been testing water-based industrial paint systems for joinery applications following these principles with further adaptations to the Dutch construction practice (KOMO tests). After withdrawal of the standard method, EN 927-4 (2000), in 2005, interest in water-vapour permeability is ...