The effect of moisture on the heat transmission through fourteen protective clothing assemblies has been analysed. The samples have been prepared in three different ways to simulate the accumulation of humidity either in the outer shell or in the inner layers. The behaviour of breathable water barriers has been investigated in particular. The assemblies have been exposed to several sources of heat (radiant, convective and contact heat) with different intensities. This study shows that for wet suits, there can be great differences in the protection given by the breathable barriers, compared with that given by coated materials. When exposed to high radiant or convective heat densities, breathable barriers offer a better protection, as a part of the humidity can be released to the outside and reduces the heat flux to the skin.