During the Great War, the institutional German propaganda targeted mainly three neutral regions in Europe, i.e. Switzerland, the Netherlands and Scandinavia. Which strategies did the German propaganda mobilize to gain support in the public spheres of these European regions? Which cultural transfers took place between them? This paper seeks to specify the key role played by Switzerland in this transnational scheme in 1914-1918. A French agent of propaganda wrote that Switzerland was a «laboratory of choice» for the German propaganda. Indeed, many German propaganda policies were first tested on Swiss grounds before they were transfered to other neutral countries, from art propaganda to «Hotelpropaganda». However, their acculturation abroad caused many difficulties, underlining the growing mental hermeticism and isolationism of public opinions in neutral countries surrounded by a war.