We have 3 styles for mattress cover:

1. 3 sides zippered (U-shape zipper) mattress protector

2. 4 sides zippered mattress encasement, this style we use exchangeable zipper. You can only take off replacement top to be washed and need not recgnize which are pairs. Eevery replacement top can match any mattress encasement. 

3. Fitted style: like fitted sheet with elastic all around