|Pest company professionals will tell you that if you can only afford one encasement it should be for your box spring. The underside of the box spring provides the perfect breeding ground for bed bugs. Encasing your mattress and box spring traps bed bugs inside and prevents bed bugs including newly hatched bed bugs from getting out. They will die inside without ever having another meal. This brand has been university tested and proven to keep bed bugs trapped inside. The specially designed zipper is escape proof, and they work.