This outer encasement allows you to revitalize your worn-out mattress. Replace the old tired layers of foam with brand new layers. This mattress shell keeps it all together while upgrading your mattress. It is designed with a zipper that goes around the top of the mattress. The zipper gives you access to your complete mattress. You will never need to buy a new mattress again! You are simply replacing the firmness, softness, or even the height of the foam to your exact preference.