A few days ago I read a thread questioning whether their insulin is still good after being in the car in cold temps for a few days. It got me wondering whether you can notice whether or not insulin had been frozen and then thawed. Anyway, I took an old pen vial and put it in the freezer for experiment (warning put it in a baggie in case the expansion from freezing pops the rubber bung off). When it is frozen, it is obvious... it solidifies and turns cloudy. However, once thrawed, there is no difference and no telltale signs of it ever being frozen. I was hoping that it would be cloudy or lumpy so that if the pharmacies/suppliers ever left it too long in the cold during shipment, that we can tell. But this is not the case. Just FYI for those who may be interested. I did not take the time to call the manufacturer to ask if insulin is still stable to use for a period once frozen or if it is ruined immediately.