We live in the Middle East and it is really hot - We have been told after refrigeration when a pen is opened keep it below 26C 79f. I have had one instance where the heat got to a pen and I could certainly tell the difference as it was much less effective. I have also had pen refills in the fridge which decided to freeze everything, the insulin went crystalline and I had to dispose of it. I now keep the insulin in the can cooler under the water cooler, it doesn't get too hot or too cold there. When we are out and about it goes into an insulated bag with a freeze-block.