Hello again Allan, Ray has made a very good point, one of the characteristics of Butane (Calor gas blue bottles)is that the the liquefied gas in the bottle has to keep vapourising to maintain the gas pressure. This process uses the latent heat of vapourisation, which it draws from the body of the liquid in the bottle. Using gas will cool the liquid (have you seen frost on bottles of propane that roofers use?) For Butane if the temperature falls below about 0C the liquid will not vapourise and the gas pressure falls to zero. Propane has exactly the same effect but it stops vapourising at about -40C, which is why it is preferred for winter use. Do not thermally insulate the gas as it relies on being able to draw heat from ambient air around it to keep the gas vapourising.