I've been on insulin since 1979 and had all kinds of insulin, short and long-acting once called "the poor man's pump"-- And I've been on an insulin pump on and off since the early 1980's when a research (DCCT) group had an extra pump, one of the early kinds where you mix regular insulin with sterile saline every day (ahem). I've now been on a pump (Medtronic) for decades and love it! I'm currently using Humalog, although I used to get Novalog--like another woman said, it's whatever insulin my healthcare provider says I should use. I'm also using a CGM, which is a humbling and great addition to everything. Here's what I've learned, and I wonder about others out there: When I'm down to the last 1/4 of my vial, the insulin gets less efficient, so I toss it out and use the new bottle. And this is even when I keep it in my fridge. I saw my blood sugars creep up as I got to the end of the bottle (I use two vials/month-).