Your sofa and chair cushions have a zipper in them, just like your favorite pair of jeans however it doesn’t mean you can clean them the same way. This brings to mind the sad faces of our customers who have tossed their cushion covers into the washing machine, gentle cycle notwithstanding, only to have a shrunken mass of fabric emerge. If they were successful in reshaping the covers, the tugging and smoothing required to place the covers correctly around the cores rarely resulted in a smooth, professional appearance.
Then, the question is, why include a zipper at all?
The zipper in the cover is there to allow the furniture factory assembly team to inset the cushion cores in a more efficient manner. Check out some older, antique furniture: their cushion covers were almost entirely hand-sewn closed. This made the cushions reversible top to bottom, but took a great deal of time and skill to be sure the seams were invisible.