Pumping produces permanent gains but most make the mistake of using too much pressure. It is important to only use enough to encourage engorgement of the corpus tissues, any more than that and you are simply stretching the skin. This allows lymph to seep in and actually inhibits real growth.
You also need positive pressure (an erection) to accomplish anything, and it must be maintained for the duration of the session.
When finishing a session, your penis should be more or less the same shape and feel as when you began, and there should be minimal decrease in sensitivity. If it feels like you’re stroking a big floppy tube sock, you’ve overdone it and should wait 48 hours before trying again.
I’ll admit, it’s fun to go overboard once in awhile and see how big you can make yourself, but the only way to make real progress is with lower pressure, erect endurance sessions.