Phenolic foam and method of manufacture thereof

A blowing agent comprising at least one chlorinated hydrofluoroolefin chosen from HFCO-1233zd and HCFO-1224yd, a hydrofluoroolefin, specifically HFO-1336mzz and a hydrocarbon, wherein the hydrocarbon is isopentane. The chlorinated hydrofluoroolefin is present in an amount of 72-92 wt%, the HFO-1336mzz is present at an amount of 5-15 wt% and the isopentane is present at an amount of 4-25 wt% of the composition. Phenolic foams made using the blowing agent composition, as well as foamble mixtures comprising a phenolic resin and the blowing agent composition are also claimed. The blowing agent is present at an amount of 1-20 parts by weight per 100 parts of phenolic resin. The phenolic resin has a water content of 10-14 wt% and the resultant foams have a closed-cell content of at least 90 wt%.