From www.Drugs.Com "storing unopened humulin
) vials or injection pens: keep in the carton and store in a refrigerator. Do not freeze.
Throw away any Insulin not used before the expiration date on the medicine label. Storing after your first use: keep the "in-use" vials or injection pens at cool room temperature, away from heat and light, and use prior to the expiration date. Throw an in-use inject".