An aqueous coating composition comprising: (i) 20 to 80 wt% of a polyurethane A obtained by the reaction of: (a) an isocyanate-terminated prepolymer formed from components comprising: 20 to 80 wt% of at least one polyisocyanate; 3 to 10 wt% of at least one isocyanate-reactive polyol of weight average molecular weight < 500 Daltons, containing at least one ionic or potentially ionic water-dispersing group; 0 to 15 wt% of at least one isocyanate-reactive polyol containing non-ionic water-dispersing groups; 17 to 77 wt% of at least one isocyanate-reactive polyol other than of weight average molecular weight ≥ 500 Daltons; 0 to 20 wt% of at least one isocyanate-reactive polyol other than or of weight average molecular weight < 500 Daltons; where,,, and add up to 100%; wherein the polyols (a) to have a total ring structure content ≥ 48wt%; and (b) an active-hydrogen chain extending compound; wherein polyurethane A has an acid value in the range of from 8 to 40 mg KOH/g and a hard segment content ≥ 40 wt% by weight of polyurethane A; and (ii) 80 to 20 wt% of a vinyl polymer B with a glass transition temperature ≥ 20°C; wherein (i) and (ii) add up to 100 %; which composition when in the form of a film exhibits a moisture vapour transmission rate (MVTR) of ≤ 500g/m 2 /24h; and where the MVTR is measured as an average after 1 and 4 days by the test method ASTM D1653-91a and as described herein, measured under tropical conditions at a constant temperature of 38°C and relative humidity (R.H.) of 90%; and with a wet film thickness of 12 micron. (i) 20 to 80 wt% of a polyurethane A obtained by the reaction of: (a) an isocyanate-terminated prepolymer formed from components comprising: 20 to 80 wt% of at least one polyisocyanate; 3 to 10 wt% of at least one isocyanate-reactive polyol of weight average molecular weight < 500 Daltons, containing at least one ionic or potentially ionic water-dispersing group; 0 to 15 wt% of at least one isocyanate-reactive polyol containing non-ionic water-dispersing groups; 17 to 77 wt% of at least one isocyanate-reactive polyol other than of weight average molecular weight ≥ 500 Daltons; 0 to 20 wt% of at least one isocyanate-reactive polyol other than or of weight average molecular weight < 500 Daltons; where,,, and add up to 100%; wherein the polyols (a) to have a total ring structure content ≥ 48wt%; and (b) an active-hydrogen chain extending compound; wherein polyurethane A has an acid value in the range of from 8 to 40 mg KOH/g and a hard segment content ≥ 40 wt% by weight of polyurethane A; and (a) an isocyanate-terminated prepolymer formed from components comprising: 20 to 80 wt% of at least one polyisocyanate; 3 to 10 wt% of at least one isocyanate-reactive polyol of weight average molecular weight < 500 Daltons, containing at least one ionic or potentially ionic water-dispersing group; 0 to 15 wt% of at least one isocyanate-reactive polyol containing non-ionic water-dispersing groups; 17 to 77 wt% of at least one isocyanate-reactive polyol other than of weight average molecular weight ≥ 500 Daltons; 0 to 20 wt% of at least one isocyanate-reactive polyol other than or of weight average molecular weight < 500 Daltons; where,,, and add up to 100%; wherein the polyols (a) to have a total ring structure content ≥ 48wt%; and 20 to 80 wt% of at least one polyisocyanate; 3 to 10 wt% of at least one isocyanate-reactive polyol of weight average molecular weight < 500 Daltons, containing at least one ionic or potentially ionic water-dispersing group; 0 to 15 wt% of at least one isocyanate-reactive polyol containing non-ionic water-dispersing groups; 17 to 77 wt% of at least one isocyanate-reactive polyol other than of weight average molecular weight ≥ 500 Daltons; 0 to 20 wt% of at least one isocyanate-reactive polyol other than or of weight average molecular weight < 500 Daltons; (b) an active-hydrogen chain extending compound; wherein polyurethane A has an acid value in the range of from 8 to 40 mg KOH/g and a hard segment content ≥ 40 wt% by weight of polyurethane A; and wherein polyurethane A has an acid value in the range of from 8 to 40 mg KOH/g and a hard segment content ≥ 40 wt% by weight of polyurethane A; and (ii) 80 to 20 wt% of a vinyl polymer B with a glass transition temperature ≥ 20°C; wherein (i) and (ii) add up to 100 %; which composition when in the form of a film exhibits a moisture vapour transmission rate (MVTR) of ≤ 500g/m 2 /24h; and where the MVTR is measured as an average after 1 and 4 days by the test method ASTM D1653-91a and as described herein, measured under tropical conditions at a constant temperature of 38°C and relative humidity (R.H.) of 90%; and with a wet film thickness of 12 micron.