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Your question leaves me scratching my head wondering WHY you want a zipper?  I have a mummy-shaped silk liner made by Cocoon that is inside my REI Magma 10 sleeping bag that has no zipper.  To MEeee, any liner is merely something to separate MEeee from the interior of my bag.  This keeps the interior of my bag clean, the silk liner is easy peasy to pull out & wash if it gets dirty or smelly from body odor.