I have had my earphones and have been using the same sleeves for about 6 months now. To me, they still seem to fit quite snug, maybe not as snug as in the beginning, but still good. How do I know when to change the sleeves? I've read that you can change them when they lose form, but how do I know when they do that?
It is quite simple. Being inherently frugal, I wash my sleeves on a regular basis, using warm water and a little Dawn dishwashing liquid. I rinse them thoroughly, pat them dry with a paper towel, and let them air dry overnight.
I change my sleeves when the foam/rubber starts to shred, or when the sleeve no longer stays on the earbud, or when the sleeve no longer provides a good seal in my ear and the bass response becomes poor.