What gets into a pillow
Sweat, skin oil, saliva and shed skin, then dust mites feeding on the last of those. A pillow gains weight over its working life and very little of the gain is filling.
A zippered protector stops all of it at the surface and comes off to be laundered, which is the whole point: the protector is washable and the pillow, realistically, is not.
Six constructions depending on what you need. 100% cotton at 280 thread count, organic cotton, Pristine® polyester for the smallest pore size, CleanAir® waterproof knit, six-gauge vinyl, and polypropylene for high-volume use.