Thermoball insulation gives warmth even when wet and is highly compressible a light yet hardwearing ripstop shell withstands the rigours of the outdoors read the full product feature list below thermoball technology thermoball technology is the new synthetic alternative to down as compressible as down clusters of round synthetic thermoball trap and retain heat within small air pockets to provide effective insulation even when wet 600 fill goose down provides warmth equal to 600 fill