The Wiggle spends most of its life in plain view — on the bed, on the couch, tied in a loop — so it should look like it belongs there. The cover gives it a second surface: linen for an everyday texture, fleece or sherpa for something to sink into.
It zips over the pillow's eucalyptus shell, so the part against your skin stays cool and the outside can be whatever the room wants. Take it off, wash it, put it back. Buy a second one and the pillow changes with the season.