I tried a cheaper solution - radiator foil - but it was very ineffective. In the end I went for an over-engineered solution. I coated my conical in 19mm thick Armaflex sheet. This was glued in place. Consequently my conical is not that shiny anymore....
Early tests suggest that with this insulation I can still hit 20C in the fermenter even when the ambient temp is around 8C. I expect system to be better than that for cooling in warm weather as the cooling system is more effective than the heating.