Transmissibility data are presented for steel and copper manganese helical springs. It is shown that for frequencies 10 to 30 times the resonant frequency of the spring-mass system, wave phenomena are important and that due to the low damping of the metals, the isolation mount may amplify the force felt by the foundation at the standing wave resonances rather than reduce it. It is shown that several modes of vibration are possible and that a one degree of freedom treatment of the problem is inadequate. The effect of coupling between the modes is discussed. Improvement of the isolation properties by coating the springs with highly viscous materials is demonstrated. It is further demonstrated that if sufficient damping is added, the value of critical coupling exceeds the actual coupling between the modes and in this case the system resembles a one degree of freedom system.