Disclosed is a thermoset, thermal insulating foams having desirable and unexpectedly low thermal conductivity, and to compositions, method and systems which use and/or are used to make such foams comprising: (a) providing thermosetting foam forming component and a blowing agent for forming predominantly closed cells in the foam, wherein the blowing agent comprises: (i) cis-1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzzm(Z)) and cyclopentane, with the HFO-1336mzzm(Z) and cyclopentane in the blowing agent together comprising at least about 50% by weight of the total of all components in the blowing agent and (ii) the weight ratio of HFO-1336mzzm(Z) to cyclopentane in the blowing agent is from about 45:55 to less than 68:32 and (b) forming foam from said provided foamable composition.