The following remarks refer to the fundamental conditions which have to be considered for the use of rubber for the mounting of engines. It is thought essential that aircraft firms should ask for information with regard to rubber components they intend to use at an early stage of the design so that faulty applications of such parts can be prevented. Figures for the permissible loads and hints for the design of rubber components are given, with special reference to the use of Buna. Some constructional features are discussed as an explanation of the advice tendered to the designer.