What's the difference between a mattress protector and a full encasement?

A protector typically covers only the top and sides (five-sided), while an encasement zips fully around all six sides of the mattress. For bed bugs and dust-mite allergies, reviewers consistently favor true six-sided zippered encasements, since open or partially covered sides defeat the barrier purpose. Several picks here, including the SureGuard and Utopia encasements, are explicitly six-sided.