The special foam screen(SFS) is a new multi-band interference technique.In order to improve its interference effect against IR and MMW guidance,the relevant theories and experiments were studied.The results indicate that the change of bubble's diameter of SFS will lead to the rapid change of the interference effect,and the smaller the bubble's diameter is,the better the interference effect will be.So to make SFS with smaller bubbles will improve the interference effect,and it can be realized by adjusting the working pressure of the equipment to discharge SFS or by changing the material formulations of SFS.