Backing foams are inserted into sealed joints in cladding systems on high-rise buildings. However, limited previous research suggested that backing rods could reduce the performance of sealed joints, in particular if the joints were moved during the early stages of sealant cure. This stimulated a comprehensive investigation of backing foams and how they influence the mechanical performance of sealed joints. Different commercially used backing foams were selected and analysed in terms of their mechanical, structural and surface properties. The influence of the foams on the static tensile and fatigue (at 1 Hz) behaviour of standard tensile adhesion joints, subjected to both static and dynamic curing over a twenty eight day period, was evaluated; this data was compared with peel forces obtained from 180° peel tests of sealant on foam specimens. It was found that the presence of backing foam could significantly reduce the fatigue performance of sealed joints.