I didn’t mean to suggest foaming only matters during reconstitution, it’s the same whenever it occurs, foam is foam. If one vial is more prone to forming foam than another in the same conditions, it’s going to be due to one of the factors I mentioned.
OP noted one formulation did it when drawing and the other didn’t, which points to something being different between the two.
That said, if you’re very gentle when reconstituting, you might avoid foaming even when a vial is prone to it, so that’s good practice generally. I saw a lot less foaming after switching to larger gauge needles for less pressure while reconstituting, 21-22 gauge. After switching to these Nokor vented (equalizes pressure as you fill or draw) reconstitution needles it doesn’t ever happen:
View attachment 370090
View attachment 370089
View attachment 370088