The CLO is the thermal resistance unit for clothing insulation, standardised in ISO 11092. 1 CLO = insulation to keep a resting person comfortable at 21°C with no wind. A typical business suit = 1.0 CLO. Summer dress = 0.2 CLO. Down jacket = 2.5 CLO. FashionFactory normalises CLO to 'warmth' (0-1) relative to down insulation. Critical for cold-climate outfit building and layering recommendations.