This aspect of insulin management is very interesting to me but, I find, very few people who pump are aware of it.
I was alerted to it by my very first diabetes educator who said that while both Novolog (aspart) and Humalog (lispro) have been tested for safety and are listed in the Medtronic pumps’ user guides, there are more detailed studies that show differences in their stability in the tubing. I didn’t think much of it then since I was using Novolog and was overall doing well in terms of BG levels. Several years later, due to insurance changes, I was forced to switch to Humalog and the new fluctuations I immediately experienced reminded me of that conversation. (I just dug out some of the literature I have encountered on the topic for a related recent post here.
So one thing I now say to anyone using a tubed pump and not getting the results they want is to try switching their insulin type.