As it is currently rather hot where I am, I thought it wise to play around with methods of temperature control before raising some seedlings. What instantly came to mind was a good old Aussie esky. Not only should it insulate the seedlings from the outside temperature, the high walls should also provide protection from the hot winds. As eskys aren't very cheap, I sourced some polystyrene boxes from the local green grocer instead. I believe polystyrene is the key insulator in eskys thus should be equivalent.
Into the poly boxes I put some plastic pots, the brand I got fitted perfectly. So impressed with their fit, I left them there for the rest of the day. The following morning when I returned, fully intending to do some planting, I was shocked to discover them in a deformed melted mess. Ponding this puzzling situation I have concluded that a polystyrene box not only keeps the heat out, but also keeps the heat in. The sun entering through the open lid obviously heated up the pots within and the polystyrene and lack of airflow kept the heat from escaping. As I can’t put the lid on, for I hope obvious reason, I am ruling this idea out.