This concerns a pair of Sorrentos, but theoretically the question isn't Sorrento-specific; any insights you can offer are welcome.
I have a pair of 42 Sorrentos. They don't quite fit, just as most of my VFFs lately haven't quite fit. I have a high instep and a narrow heel, which generally gives me two options; I can buy a pair of 41s in a style, and hope the upper stretches out, or I can buy a pair of 42s and deal with a loose heel cup. With these Sorrentos, I went with the latter.
However, in theory, I like these Sorrentos well enough to put in a little effort to make them fit better. When I was a kid, we would always put cotton padding in the heels of my shoes to make them fit a little better. You can buy this sort of padding almost anywhere that sells shoes; roughly the consistency of a cotton ball as I recall.
I'd like to do something similar with these Sorrentos, but it's not quite so cut and dry. With a regular pair of sneakers, it doesn't really matter what material you use for padding. But for a pair of VFFs which will (ideally) be washed regularly, I need something that is either (a) machine washable, or (b) disposable, and removable to a point where it doesn't damage the shoes. The cotton padding I remember from my childhood fit neither of these categories; it was super stringy and cheap cotton, and it came with a sticky backing that was sure to take part of the shoe with it if removed.
Does anybody have any ideas here? Surely this sort of issue has been tackled here before.