Eli Lilly and Company is an American pharmaceuticals giant from Indianapolis. Eli Lilly has been producing insulins commercially since 1923.
Studies done on all Lilly vialed insulins--Humulin, Iletin, and Humalog, show that the stoppers have sufficient resealing properties to maintain a good seal after 100 punctures. What this means to you is that the insulin will stay potent longer.
More on the company and its products here.