Reply from our Silentnight Expert:
If your mattress cover does not have a label on it with washing instructions then do not attempt to clean it. Whilst the cover is zipped, if you did remove it you would find it extremely difficult to put back on. The mattress core is inserted into the cover using specialist machinery and not by hand. These covers are not suitable for machine washing or dry cleaning.
We recommend the use of a good mattress protector to keep your mattress clean.