It depends very much on the foaming agent you use. If it is water you may chose a surfactant like TEGOSTAB B8433, if you use a mix of water amd physical foaming agent like pentane or a flourinated hydrocarbon you have to try with several types as their way and quality of action depend on the composition (ratio of water and hydrocarbon). Further, you have to adjust your catalytic system. In case of water only you may use a mixture of DABCO and tin dioctoate (usually 0.9 to 0.3 g /100 of A component), in case of mixing the foaming agents you have to adjust and use probably another catalytic system, e. h. including PC CAT TMG or PC CAT NP 50.