I don't believe they change your sheets or duvet cover during the time you on onboard. They do change them between passengers though. The morning we disembarked, I pulled the curtains back to let the sun in. When I did, I saw two clean sets of sheets, pillowcases, and duvet covers. The bedspreads do not get washed often enough though. I have a problem with that too. I wish they would stay on top of that. Maybe they should pull them all the day before you disembark, wash them, and keep them until the morning when it's time to change the beds.